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2734A
DIRECT VOLTAGE
REFERENCE BANK
OPERATION AND
MAINTENACE MANUAL
9955 Mesa Rim Rd.
VALHALLA
tlE SCIENTIFIC San Diego,Ca 92121
Phone (6 19)457 -SSZ6
Telex 181 75O REVTSED 1 / 87
CERTIFICATION
valhalla scientific, Inc. certif ies that this instrument lYas
thoroughly tested and inspected and found to meet it's
published specif ications when it was shipped f rom the factory.
valhalla scientif ic, Inc. further certifies that it's calibration
measurements are traceable to the National Bureau of Standards
to the extent allowed by NBS's calibration facility.
WARRANTY
The warranty period for this instrument is stated on your
invoice and packing list. Please refer to these to determine
appropriate warranty dates. We will repair or replace the
instrument during the warranty period provided it is returned
to valhalla Scientif ic, Inc. f reight prepaid. No other warranty
is expressed or implied. we are not liable for consequential
damages. Permission and a return authorization number must
be obtained directly from the factory for warranty repair
returns. No liability will be accepted if returned without such
permission.
TABLE OF CONTENTS
SECTION NUMBER PAGE
SECTION I- UNPACKING AND INSTALLATION t-l
SECTION II - SPECIFICATIONS 2-1
SECTION III - AVAILABLE OPTIONS 1l
SECTION IV - FRONT PANEL CONTROLS AND CONNECTIONS :1
t- I
|
SECTION V - REAR PANEL CONTROLS AND CONNECTORS 5- l
SECTION VI - MANUAL OPERATION o-l
SECTION VII - REMOTE OPERATION l-l
SECTION VII - CALIBRATION 8- r
SECTION IX - MAINTENANCE AND TROUBLESHOOTING 9-l
SECTION X - THEORY OF OPERATION r0- r
SECTION XI - PERFORMANCE VERIFICATION Il-l
SECTION XII - USEFUL HINTS t:- I
SECTION XIII - MANUAL CHANGE INFORMATION l3- r
SECTION XIV - SCHEMATIC AND ASSEMBLY DIAGRAMS t4- I
SECTION XV - PARTS LISTS r5- l
l-l
SECTION I. UNPACKING AND INSTALLATION
1.1 Unpacking
If the shipping carton is damaged, request that the carriers' agent be present when the
2734A is unpacked. If the 2734A appears damaged when unpacked, then notify the
carriers' agent who should authorize repairs before the 2734A is returned to Valhalla
Scientific or Service Center. Even if the 2734A appears undamaged, it may have suffered
internal damage in transit that may not be evident until the 2734A is operated or testecl
to verify performance. If the 2734A fails to meet the performance specifications in
Section II, then notify the carriers' agent and Valhalla Scientific or Service Center.
Retain the shipping carton for the carriers inspection. DO NOT RETURN EQUIPMENT
TO VALHALLA SCIENTIFIC OR ANY OF ITS SERVICE CENTERS PRIOR TO OBTAINING
AUTHORIZATION TO DO SO.
1.2 Initial Adjustments
The only adjustments required prior to operation of the 2734A are the correct selection
of the local power source voltage and to verify that the correct fuse for this voitaee is
fitted. The supply voltages and fuses are listed below:
105 to l28VAC 50/60H2 I Amp Slo Blo Fuse
210 to 256VAC 50/60H2 0.5 Amp Slo Blo Fuse
The user should note that both fuses are contained within the power socket on the rear
panel, and are automatically selected when the power line voltage selection is macle.
Either 20mm. or 1.25" fuse sizes may be used.
THE 2734A IS SHIPPED IN ''TRANSIT MODE'" POWERED BY INTERNAL BATTERIES. IT IS
RECON{NIENDED THAT THE UNIT HAVE POWER APPLIED AS SOON AS POSSIBLE AFTIII
UNPACKING IN ORDER TO MAINTAIN THE TRACEABILITY OF THE SPECIFICATION.
ENSURE THAT THE CORRECT SELECTION IS MADE PRIOR TO APPLYING POWER TO-|IIE
27 31A.
1.3 Instructions for Bench Use
The 2134A is delivered for operation in bench use and special instructions for use in this
manner are not required. However, before connecting the 2134A to the AC power
source, the user should verify that the power cord is equipped with a three-terminal
connector (see the Safety Precautions in 1.5).
1.'1 Instructions for Rack Mounting
Optional rack mounting brackets are available for mounting the 2734A in a standard l9'
an,rinment ranlq. These are listed in Section III of this manual. The size and weieht of
rrrqrruqr, r tru JIz!
the 2134A dictate that the unit should be supported on both sides along it's enrire length
(by the use of "trays" or "slides"). If it is to be transported while mounted in a rack
thEN it MUST BE SUPPORTED SO AS TO PREVENT UPWARDS AND DOWNWARDS
MOVEMENT.
l-t
The user should note that the specifications of the 2734A become degraded at high
temperatures. It is recommended that sufficient room be allowed for airflow around the
2734A. This may be achieved by placing at least l.75" high blank panels above and
below the 2734A in the rack.
If the unit is placed beneath the 2734A has an exceptionally hot exterior top surface,
and it is not possible to alter its location, the user is recommended to fit an aluminum
"reflector" plate between this unit and the 2'734A.
Under no circumstances should the ambient air temperature surrounding the 2718A be
allowed to exceed 50C while in operation or 70C while not in operation.
1.5 Safety Precautions
The power connector should be a three-contact device meeting the safety requirements of
the area in which the 2734A is to be used, and should only be mated with a three-
contact connector where the third contact provides ground connection. If power is
provided through an extension cable then the ground connection must be continuous
throughout this cable to the 2734A.
FAILURE TO PRO\/IDE A CONTINUOUS GROUND CONNECTION TO THE 2734A I\{AY RENDER
THE UNIT UNSAFE FOR USE.
t-2
SECTION II . SPECIFICATIONS
2.1 General
The specifications of the 2734A Direct Voltage Reference Bank are listed in the followine
paragraphs.
2.2 Stability
The stability figures given below are valid for ambient temperatures between l8 and 28C
and assume continuous application of power.
OUTPUT 30 days 90 days 180 days I year
l.0V l.Oppm 2.0ppm 3.0ppm 5.0ppm
l.0l 8V I .Oppm 2.0ppm 3.0ppm 5.0ppm
Y7 0.4ppm 0.8ppm l.6ppm 3.0ppm
lOV 0.5ppm l.3ppm 2.5ppm 4.0ppm
Each2734A is shipped "hot" (in transit mode) from Valhalla Scientific in San Diego, CA,
USA, the initial adjustments made by Valhalla Scientific acheives a worst case traceable
error against the US national volt of l.5ppm. This figure may be used with the
specifications above as a traceable uncertainty if the 2734A has AC power applied within
48 hours (144 hours if shipped in option TC34) of leaving Valhalla Scientific Inc and
following 2 hours stabilization. Each 2734A is shipped with the actual measured values
of each output quoted on a certificate with 0.lppm resolution.
2.3 Settability
Each of the 2734A outputs may be adjusted over the range and with the resolution shorvn
in the table below :
OUTPUT ADJUSTMENT RANGE RESOLUTION
l.OV l0ppm total 0.02ppm
l.0l8v lOppm total 0.02ppm
Y7 @ refs) 70ppm total 0.l4ppm
Y7 Q ref) 280ppm total 0.56ppm
lOV 5ppm total 0.0lppm
2.4 Temperature Coefficients
The temperature coefficients listed below are applicable within the 0 to 18C and 28 to
40C temperature ranges following l5 minutes of stabilization at the new ambient
conditions.
OUTPUT COEFFICIENT
l OV 0.Ippm/C
.018V
I 0.Ippm/C
Y7 0.02ppm/C
lOV 0.05ppm/C
z-l
2.5 Temperature Shock
Ambient temperature changes of greater than l0C per minute may cause a non-
accumulative change in output voltage of no greater than 0.0lppm/C change.
2.6 Output Drive and Resistance
The output resistance of each output at the respective terminal is as listed in the table
below :
OUTPUT MAX DRIVE RESISTANCE
l.OV 857.14 ohm +/- 0.0050/o
l.0l8v 869.95 ohm +/- 0.0050/o
Y7 3mA 0.05 ohm maximum
lOV l2mA 0.005 ohm maximum
Any (or all) of the outputs may be shorted indefinately, are protected against the
external application of transients up to 1200V peak, and may continuously source or sink
up to l00mA of current without permenant damage.
2.7 Supply Regulation
The maximum change in output voltage caused by a change in supply voltage from the
minimum to the maximum value/frequency specified is less than 0.05ppm following a l0
second delay. The maximum change in output voltage caused by a change in supply
source is less than 0.05ppm following a l0 second delay.
If a complete loss of power occurs then a non-accumulative change in output voltage of
less than 0.lppm may occur following stabilzation after re-application of power.
2.8 Output Noise
OUTPUT 0.01 to l0Hz BANDWIDTH l0Hz to 20KHz BANDWIDTHI
l.0V 0.luV peak maximum 3uV RMS maximum
l.0l8v 0.luV peak maximum 3uV RMS maximum
Y7 luV peak maximum l0uV RMS maximum
lOV luV peak maximum l0uV RMS maximum
I Add 2uV RMS maximum if operating from AC power source
,ta
2.9 Miscellaneous
Settling time to within 0.lppm of final value :
Transit to normal mode : < l0 minutes
Fully drained batteries to operational : Change in suplly source : < l0 seconds
Internal Batteries :
TYPe Sealed Lead-Acid
Charging time l2 hours typical (36 hours maximum)
Replacement Interval 5 years recommended
Normal mode life At OC l5 hours minimum
At 20C 24 hours minimum
At 40C 40 hours minimum
Transit mode life At 0c 30 hours minimum
At 2OC 48 hours minimum
At 40C 100 hours minimum
External DC Supply :
Voltage range +24 to +40VDC
Current drain 0.2A typical at 20C (0.8A maximum)
Protection Internally protected against reverse connection ancl
fuse protected (l Amp) against over voltage.
AC Line Supply :
Voltage/Frequency 105 to l30V or 210 to 260VAC at 45 to 440kIz.
Power requirements 60VA maximum while charging, 20VA maxinrunr irr
normal operation.
Safety : Designed to comply with IEC-348 and IJL|244
Maximum voltages : Guard terminal to Common terminal : 50V peak maximum
Guard to Chassis Ground : l00V peak maximum
2.10 Physical
Size : 89mm H x432mmW x432mm D(3.5" x 17" x 17")
Weight : l6Kg (35 Lbs) Net
t9Ke Q2 Lbs) Shipping (without TC34)
29Ke (64 Lbs) Shipping (with TC34)
z-)
2.1 1 Environmental
Temperature Range : :
Operating 0 to 40C
Storage : -20 to + 60C
Humidity : 0 to 95o/o RH at temperatures below 35C
0 to 700/o RH at temperatures between 35 and 40C
Altitude -1000 to 10.000 ft.
Vibration Per MIL-T-28800C, Type III, Class 5, Style E
2.12 Recommended Calibration Interval
The calibration interval for the 2734A is dependent on the accuracy the user wishes to
maintain. The user should consult the accuracy tables in 2.2 to determine the number of
days between calibrations to obtain the required accuracy.
L-.+
SECTION III - AVAILABLE OPTIONS
3.1 General
This section describes several options available from Valhalla Scientific to increase the
utility of the 2734A.
3.2 Option BBL
Option BBL is a dual shielded cable equipped with banana plugs. It is 48 inches long
with dual banana plugs of the highest quality and low leakage. This cable is
recommended whenever accuracies of greater than luv are desired.
3.3 Option RSK-3
Option RSK-3 is a heavy duty rack slide kit which allows simple mounting and removal
of a 2734A in an equipment rack. Option RX-3 rack ears are also recommended. It is
recommended that option RSK-3 be factory installed.
3.,1 Option RX-3
Option RX-3 provides all parts required for mounting the 2734A in a l9 inch equipment
rack.
3.5 Option SL-48
Option SL-48 is a 48 inch long shielded cable terminated at each end by high quality
gold plated copper spade lugs. The use of this option is recommended whenever
acuuracies of greater than 0.5uV are desired.
3.6 Option SP-2
This option provides a selection of the most likely parts to fail during the first two
years of operation.
3.7 Option TC-34
This option provides a rugged carrying case and rechargeable battery supply for the
2734A. The use of this option is strongly recommended if the 2734A is to be used for
repeated transportation or whenever the utmost transfer accuracv is desired.
3-l
SECTION IV - FRONT PANEL CONTROLS AND CONNECTORS
4.1 General
This section outlines the use of each of the front panel controls and connectors, the
user is advised to read Section VI to obtain full descriptions of the method to operate
the 2734A.
The paragraph numbers used in this section correspond to the reference numbers used in
figure 4- l.
J.1.1 "CHASSIS GROUND" Terminal
This terminal is connected directly to the chassis of the 2734A and should be grounded
whenever the 2134A is operated from AC line and the line cord does not contain a
ground connection. It is also recommended that this terminal be grounded whenever the
2734A is operating from DC supply (internal or external) and no AC line cord is presenr.
.1 .1.2 ''''TRANSIT MODE'' LED
This LED is illuminated whenever the 2734A is in "Transit Mode" 1r." S..tions V and VI
for details). This LED being illuminated indicates that the 2i34A is not ready for use
{.I.3 ''BATTERY CHARGING'' LED
This LED is illuminated whenever the internal batteries in the 2i34A are being charged
(from the AC supply). This LED being illuminated indicates that the internal bateries clo
not have sufficient charge to maintain the battery life specifications in paragraph 2.9.
4.1.4 ''OVEN FAULT'' LED
This LED is illuminated whenever the internal oven temperature exceeds the regulation
temperature by more than 5C. This LED being illuminated indicates that the 2134A has
not yet settled from high storage temperatures or, if the condition prevails, the internal
temperature regulation circuitry is faulty. Whichever the cause the 2734A is not ready for
use if this LED is illurninated. This LED is always extinguished whenever the 2734A is
in the "Transit Mode".
.I .I.5 ''AC ON'' LED
This LED is illuminated whenever an AC power source is present and the AC power
switch (on the rear panel) is in the ON position (see paragraph 5.1.1).
,{.1.6 "BATTERY O.K." LED
This LED is illuminated whenever the internal batteries or external DC supply exceeds
the minimum required for correct operation of the 2134A. This LED being extinguis6ecl
indicates that the 2734A is not ready for use and that the LED indications may be
invalid.
4-l
4.1.7 ''OVEN READY'' LED
This LED is illuminated whenever the internal oven temperature is within 0.5C of its
final value. This LED being extinguished indicates that the 2734A is not ready for use.
4.I.8''CALIBRATION ACCESS COVER''
This removable cover gives access to the calibration adjustments. See section VIII for
details.
4.1 .9 "1.0V", "1.018V", "Y2", "10Y", "COMMON" and "GLIARD" Terminals
These terminals provide the voltage outputsfrom the 2734A and the means to guard the
internal circuitry within the 2734A from common mode voltages.
4-2
SECTION V - REAR PANEL CONTROLS AND CONNECTORS
5.1 General
The functions of the rear panel controls and connectors are described in the following
paragraphs. The paragraph numbers correspond to the reference numbers of Fieure 5-1.
5.1.1 "INSTRUMENT POWER" Connector
This connector contains the AC power connector, AC power voltage selection switch, AC
power ON/OFF switch and fuses. The AC power switch is in the ON position if the " l,'
is depressed, and is in the OFF position if the "0" is depressed. The AC line voltage
selection is 105 to l30v if 'll0-120v'is lowermost, and is 210 to 260v if ,,220-240y,,is
lowermost. The selection may only be made if the power cord is not inserted into the
connector, this is also the case if the fuses are to be changed or inspected. See figure
5-2 for details on changing the fuses or line voltage selection.
5.1.2 "OVEN MODE" Switch
This switch selects either "Transit Mode" or "Operate Mode" of operafion. Transit mode
reduces the internal power consumption of the 2734A to extend the battery life of the
unit while maintaining power to, and the temperature of, the internal references. The
"OPERATE" mode must be selected whenever it is desired to tise the 2l34A.
5.1.3 "EXTERNAL BATTERY" Terminals and "FUSE"
The terminals provide the means by which an external DC power source may be provided
to the 2734A. The fuse provides protection for the internal circuitry against excessive
voitages on these terminals.
5-l
SECTION VI - MANUAL OPERATION
6.1 General
This section provides information regarding the normal use of the 2734A and the
transportation methods recommended for use of the 2734A in transfer measurements
between laboratories.
6.2 Power Connections
The 2734A has internal batteries to maintain all circuitry within the unit in the absence
of sufficient external AC or DC power, these batteries are automatically charged (if thel'
require it) from the AC power input if it is connected and turned ON. The switch over
from one power source to another is automatic and virtually transient free.
Inspection of the specifications (see Section II) shows that the accuracy 2734A js
virtually unaffected by the power source, thus the user may select the most convenient
power source for the application.
6.3 When is the 2734A Ready for Use?
The 2734A is ready for use whenever the following conditions exist :
i) The BATTERY O.K. LED is illuminated
AND
ii) The OVEN READY LED is illuminated
AND
iii) The OVEN FAULT LED is extinguished
AND
iv) The TRANSIT MODE LED is extinguished
AND
v) The CALIBRATION ACCESS COVER is in place
6.,1 Using the GUARD Terminal
The GUARD terminal on the front panel of the 2734A is internally connected to a guarcl
"box" completely surrounding the reference and output amplifier circuitry of the 2:'34A.
It should always be connected to a low impedance node, particularly if the 2i34A js
being operated in excessively electrically noisy environments. In general connection to
the COMMON terminal of the 2734A will be sufficient, however it may be necessary to
connect this terminal to chassis ground. NEVER LEAVE THIS TERMINAL
DISCONNECTED WHEN USING THE 2734A.
6-l
6.5 Making Connections to the 27344
The terminals on the 2734A are made from high quality gold plated tellurium copper, thus
thermal emfs are reduced to the least possible. Thermal emfs can however be produced
in the connections to the terminals if the wires used are not made from pure copper
and/or act as heat conductors to or from the terminals. As with any piece of electronic
equipment, the internal temperature of the 2734A is higher than that of the surrounding
air, particularly if the unit is near to an air-conditioning duct, thus if the connecting
wires are good conductors of heat then thermal emfs can be produced at the contact
point to the terminals. Thus the following connection wires types are recommended :
i) Accuracies in excess of luV : Good quality "dual" banana type leads mt1, be
used.
ii) Accuracies in excess of 0.5uV Good quality copper spade lug terminated
shielded cable.
iii) Best possible accuracies Twisted pair of 24AWG (or smaller) high prritr
solid copper conductor, Teflon (or simular)
coated wire.
The user should note that the type i) cable offers ease of use and relatively low
impedance levels (typically 5 to 25 milliohms) and good performance at the V7 and l0V
output levels, type ii) cable offers good general purpose use at all voltage levels and
very low impedances (typically 3 to l0 milliohms), while type iii) cable offers the best
possible performance at the cost of ease of use and impedance levels (typically 25 to 200
milliohms).
6.6 Transportation of the 2734A
There are a range of methods for transporting the 2734A while maintaining the integrit)'
of the output voltage specifications, the various methods for each type of movement are
described below. Using these methods of shipping 2734A's transfer accuracies of better
than 0.lppm can be achieved, if less accuracy and integrity is required then less
precautions need be taken.
6.6.1 Short-Range Moiements (no temperature extremes, less than t hour)
For short movements within a building the internal batteries and thermal lagging
provided within the 2734A are provided for protection against loss of integrity during
this type of movement, thus no special precautions are necessary other than ensuring
that the batteries have sufficient charge for the movement (check that the BATTERY
CHARGING LED is extinguished when powered from AC line prior to disconnection and
movement). For this type of movement it is not necessary to select TRANSIT mode, thus
minimal stabilzation time is required when the 2734A reaches its final destination (as
soon as the OVEN READY LED is illuminated the 2734A is ready for use, if no major
temperature differences are encountered then this will be immediate).
6-2
6'6.2 Short or Medium-Range Movements (exposure to ambient changes, less than 12 hours)
For short or medium range movements where the 2734A may be exposed to large ambient
changes or adverse weather conditions (i.e. movement from one building to another) or
the movement may take over one hour (but definitely less than l8 hours) then the
internal battery supply may still be used and TRANSIT mode is unnecessary, however it
is recommended that the unit be shielded from the weather conditions and temperature
shocks by wrapping it in weather proof material (plastic "bubble pack" material is
excellent). Upon reception of the 2734A after the movement the unit should be powered
from AC power as soon as possible to recharge the internal batteries, the 2734A wili be
ready for use as soon as the OVEN READY LED is illuminated (typically within 1 or 2
minutes, immediately if the conditions were not severe).
6.6.3 Long-Range Movements (less than 30 hours)
For long range movements or whenever it is possible that the 2734A may be left without
AC power for extended periods of time (but less than 30 hours, e.g. between facilities)
then the precautions indicated for medium range movements (6.6.2 afove) should be
followed with the addition of the selection of TRANSIT MODE prior to shipment. It is
also recommended that the 2734A be shipped in a shipping container capable of
withstanding typical shipping shocks (it is recommended that the user retain the Valhalla
Scientific shipping container for this purpose). If the 2734A is to transported in a car
then it is recommended that it is placed in the passenger compartment, rather than in
the trunk, and should not be left in the vehicle overnight, to protect the 2734A from the
extremely wide range of temperatures and humidities present in the trunks of cars. If
the 2734A is not be "personally" transported then it is recommended that the user clearly
mark receiving intructions (i.e. instructions to unpack the unit and apply AC power as
soon as possible) on the exterior of the shipping container.
NOTE : IF THE TRAVEL MAY BE DELAYED BY PREVAILING WEATHER CONDITIONS
(E.G. AIR TRAVEL DELAYS DUE TO SNOW ETC.) THEN THE PROCEDURE IN 6.6.4 IS
RECOMMENDED.
6.6.4 Long-Range Movements (less than 6 days)
For very long range movements or whenever the utmost integrity is required then the
user should place the 2734A in an option TC-34 carrying case where both the unit ancl
the carrying case have been fully charged (neither unit has a CHARGING LED illuminatecl
when powered from AC power). The option TC-34 offers protection against shipping
damage and thermal shock, while powering the 2734A for the entire time (the 2i34A
should have TRANSIT MODE selected if the transit time is longer rhan 3 days).
6.6.5 Very Long-Range Movements and/or Very Adverse Conditions
The 2134A has been designed to withstand a very wide range of temperatures with a
minimum of user support, however some conditions may adversely affect the integrit)' of
the performance. If very adverse conditions are expected during transportation of the
2134A then the user is recommended to consult the nearest Valhalla Scientific Service
Center prior to shipping the 2734A. The user may wish to individually measure each of
the four internal references prior to shipment and then compare their measurements upon
reception, if any reference movement does occur it is extremely unlikely that all four
6-3
references will be affected, thus the integrity of the absolute value of the Y7 output
voltage can be maintained since no major elements effect this output other than the
references themselves, the other outputs can then be ratiometrically calibrated (see
Section VIII) at the receiving end.
i) Possibility of very low temperatures (e.g. travel in the Polar regions).
The internal circuitry is ovened even when in TRANSIT mode, thus even
temperatures as low as -40C will not adversely affect the references and outpur
amplifiers. However, the internal lead-acid batteries will not withstand these
temperatures thus they should be removed and some form of external DC power
source used to maintain the internal temperature during movement. Lithium or some
Nickel-Cadmium batteries have excellent performance at sub-zero temperatures and
are recommended. The possibility of extreme temperature shock exists in these
conditions, thus the user is strongly recommended to thoroughly thermally insulate
the 2734A.
ii) Possibility of very high temperatures (e.g. travel in the equatorial desert regions).
Experience with semiconductor references has shown that temperatures in excess of
85C may cause shifts in their voltages, also the internal lead-acid batteries may be
damaged by such extreme temperatures. Thus the user is strongly recommended to
remove the internal batteries and to ensure that the 2734A is mainatined away from
direct sunlight while being transported in these conditions (in general, the ambient
air temperature does not attain these very high temperatures but direct sunlight can
cause surfaces to exceed even l00C in these conditions).
iii) Possibility of extended time periods.
The external DC power input may be connected to any convenient source of power
between 24Y and 40VDC and the internal circuitry of the 2734A will maintain
operation for inputs down to I5VDC under normal conditions, thus the user may
construct any power source if the length of the journey is known. If the journey
(or storage) of the 2734A becomes extensively extended and the power source
becomes ineffective then the 2734A is specified to yield a worst case change in
output voltage of 0.lppm which is adaquate for all but the most decerning of
measurements.
6.7 Typical Connection.s and Usages
Connections and typical usages of the 2734A are shown in the various figures at the end
of this section. The user should note that when two (or more) 2734A units are
connected in series to obtain higher voltages then the units should be powered by their
internal battery supplies and the CHASSIS GROUND terminals left open circuit for the
bCSt iN PCTfOTMANCC (NOTE - THIS MAY CAUSE THE CHASSIS TO HAVE DANGEROUS
POTENTIALS, CARE MUST BE TAKEN).
6-4
SECTION VII - REMOTE OPERATION
THIS SECTION IS INTENTIONALLY LEFT BLANK FOR PROPOSED FUTURE DEVELOPEMENT.
7-l
SECTION VIII - CALIBRATION
8.1 General
The 2734A is calibrated with the covers on. Access to the adjustment potentiometers
and switches is made by removing the calibration access port cover located on the front
panel. A calibration certificate sticker may be placed over the access port cover to
preserve calibration integrity.
8.2 Removing the Calibration Cover
To remove the calibration access cover, gently pull out the two plungers on the cover
about 1/8". Pull evenly on the two plungers to remove the cover. To replace the cover,
ensure that plungers are in the withdrawn position. Line the grommets up with the
holes in the front panel and gently press the cover into place. Push the two plungers in
until they are seated.
8.3 Calibration Following Component Replacement
If a component has been replaced, damaged by misuse, or a long period of time has
elapsed since the factory calibration, the calibration potentiometers may not have enough
range. The range of the potentiometers may be moved by changing the positions of the
shorting plugs on the resistor banks in the reference enclosure. Access to these plugs is
made by removing the upper front bezel, the instrument top cover, the reference
enclosure top cover and then the upper insulation covering (see figure 8-l).
8.4 General Calibration Philosophy
The calibration of the 2734A can be acheived in one of three differing ways, dependant
on user requirements :
i) For most usages and for routine periodic calibration of the 2734A it is not
necessary to actually correct for any deviations in the output voltages of the
2734A, it is only required to exactly "know" and record the actual values. In this
case it is not necessary to remove the CALIBRATION ACCESS COVER, it is only
necessary to measure the actual output voltages. The procedure for performing this
is dependant on personal preference and the equipment available however the
method used by Valhalla Scientific Inc. is outlined in paragraph 8 5 below.
ii) Where it is not necessary to adjust the outputs to exactly the correct, nominal,
voltages (similar to i) above) but the integrity of the 2734A absolute voltage is ro
be checked then measurements of each individual reference "cell" and checking of
the averaging of these "cells" will be required. In this case the CALIBRATION
ACCESS COVER must be removed, however no adjustments of the potentiometers
will be required. The procedure which Valhalla Scientific Inc. uses to perform this
is outlined in paragraph 8.6 below.
iii) When it is required to correct for deviations of the actual output voltages from the
nominal or realign the individual reference "cells" then adjustments of the internal
potentiometers will be required and the CALIBRATION ACCESS COVER must be
removed. The procedure which Valhalla Scientific Inc. uses is outlined in paragraph
8.7 below.
8-l
8.,1.1 Pre-Calibration Preparation
Very little preparation of the 2734A is required prior to calibration, however the
following items should be followed :
i) The 2734A should have the internal batteries fully charged (CHARGING LED should
be extinguished).
ii) The 2734A should have been stabilized in the calibration environment for at least
two hours prior to making measurements.
iii) Final calibration measurements should be made with all of the covers in place, 30
minutes stabilization should be allowed following replacement of the top cover. If
accuracies of better than 0.2ppm are required then measurements must be made with
the CALIBRATION ACCESS COVER in place (5 minute stabilization is recommended).
8.5 Measurement of Actual Output Voltages Without Adjustment
This paragraph describes the method by which Valhalla Scientific Inc. measures the actual
voltages present on each of the four outputs from the 2734A. The user may use any
method which is acceptable for the accuracy level which is required in the actual
application, the user may also wish to record the measured values (along with some
computed ratios) in the same manner as Valhalla Scientific Inc. does on a form similar to
that shown in Table 8-l (this may aid the user in determining error sources should a
discrepancy occur). The measurements may be performed in any order since no
adjustments are performed. Throughout these procedures it is assumed that the user is
conversant with the normal use of the equipment listed, and that the equipment is in
good working order and has been recently calibrated.
8.5.1 Measurement of the 1.018V Output Voltage
Equipment Used : i) Standard Cell with exact value known.
ii) Valhalla 2720G5 or HSR.
Step I Short the nullmeter terminals on the 2720 and short them to the OUTPUT
LOW terminal on the 2720 using 24AWG bus wire or similar. Turn on the
nullmeter and allow any thermal emfs to subside. Zero the nullmeter.
Step 2 Remove the shorting wires on the nullmeter of the 2720. Select a DIVIDED
output voltage from the 2720 of the same value and polarity as the selected
standard cell. Turn off the nullmeter. Using 24AWG teflon coated connection
wires (or similar) connect the standard cell to the 2720 as follows :
Cell LOW to 2724 OUTPUT LOW
2720 OUTPUT HI to 2720 Nullmeter HI
Cell HI to 2720 Nullmeter LO
Select the AUTO NULL mode of operation on the 2720 with a division ratio ot
+0.25, select for the deviation to be displayed in PPM. Note the settled value
of deviation displayed on the 2720. Turn off the nullmeter and remove the
connections to the nullmeter (be careful not to short them).
8-2
Step 3 Repeat Step 2 with the following connections (ensure that the cell voltase
value is re-entered on the 2720\:
Cell LOW to 2720 OUTPUT LOW (should be already present)
2720 OUTPUT HI to 2720 NULLMETER Lo
Cell HI tO 2720 NULLMETER HI
Select the AUTO NULL mode of operation on the 2720 with a division ratio of'
-0.25 (NOTE POLARITY). Note the settled value of deviation displayed on the
2720. Turn off the nullmeter and remove the connections to the nullmeter (be
careful not to short them).
Step 4 Repeat steps 2 and 3 for each cell in the cell bank (the user may make as
many measurements as wished), separately noting each ppm deviation of the
2720.
Step 5 Calculate the mathematical average of all of the ppm deviations recorded for
the steps 2 and 3, i.e. add up all of the deviations and divide the result by
the number of measurements taken. THIS DEVIATION IS THE ERROR oF I HE
I VOLT DIVIDED RANGE OF THE 2720 AND MAY BE RECORDED IN TTIE
CALIBRATION RECORD OF TIts,E 2720IF DESIRED (NEGATIVE RESULT
INDICATES THAT T}lE 2720 OUTPUT IS HIGHER THAN EXPECTED). NOIE
this calculated ppm deviation (be careful to record the polarity of the error.
If desired the standard deviation of the data may also be calculated (this gives
an indication of the random error in the measurement). THE usER MAy
ALSO NOTE THAT INTER-CELL COMPARISONS MAY BE ACHIEVED A-f THE
SAME TIME, THE AVERAGE OF EACH CELL'S STEP 2 AND 3 DEVIATION
MAY BE INTER-COMPARED YIELDING THE ACTUAL PPM DEVIATION F'RON,I
CELL TO CELL.
Step Remove all connections from the 2720 and the standard cell bank.
Step Select a DIVIDED output from the 2]20 of +1.01g00000 v then enter rhe ppnr
deviation obtained in step 5 (ensure that the same polarity is used) . The 2l'20
output voltage is thus set to EXACTLY 1.01800000 V. The worsr case error in
the 2720 output is 0.25ppm (typically < 0.lppm).
Step 8 Using the same wires as used to connect the standard cells above, connect the
2720 to the 2734A as follows :
2734A COMMON tO 2720 OIJTPUT LOW
2720 OUTPUT HI to 2720 NULLMETER HI
2t34A l.0l8V to 2720 NULLMETER LOW
Select the AUTO NULL mode of operation on the 2720 with a division ratio of
+0.25, select for the deviation to be displayed in PPM. Note the settled value
of deviation displayed on the 2720. Turn off the nullmeter and remove tl.re
connections to the nullmeter (be careful not to short them).
8-3
Step 9 Repeat Steps 7 and 8 with the following connections (ensure that the value is
re-entered on the 2720):
2734A COMMON to 2720 OUTPUT LOW (should be already present)
2'720 OUTPUT HI to 2720 NULLMETER LO
2734A l.0l8V to 2720 NULLMETER HI
Select the AUTO NULL mode of operation on the 2720 wlth a division ratio of
-0.25 (NOTE POLARITY). Note the settled value of deviation displayed on the
2720. Turn off the nullmeter and remove all connections.
Step 10 Compute the average of the two deviations recorded in steps 8 and 9. This
value is the ppm deviation of the l.0l8V output of the 2734A from the nominal
value, a negative value indicates that the 2734A actual output voltage is lower
than nominal.
Using the above procedure the worst case error is 0.5ppm, however due to averaging of
measurements and the procedure used the nominal error (RMS of errors) is less than
0.3ppm worst case and typically less than 0.lppm (plus the traceability error of the
standard cells).
8.5.2 Measurement of the 1.0V Output Voltage
This measurement follows the same procedure as shown for the l.0l8V output in
paragraph 8.5.1 above, however a voltage of 1.00000000 V is used in steps 7,8 and 9, and
the error is increased (due to the slightly extended range over which the linearity of the
2720 is used) by 0.05ppm worst case. Note that if the t.0l8V output was measured
immediately preceding this measurement then steps I through 6 are unnecessary, the data
calculated in step 5 of 8.5.1 being re-used.
8.5.3 Measurement of the l0V Output Voltage
The user should note that this procedure is basically the same as that performed for the
l.0V and l.0l8V outputs and is fully explained only for clarity.
Equipment Used : i) Standard Cell with exact value known.
ii) Valhalla 2720G5 or HSR.
iii) Precision l0:l divider (l0.l8V:l.0l8V and l0V:lV)
.
NOTE : Throughout this procedure it is assumed that the divider has a relatively high
input impedance and thus four terminal connections are not required (for a
Fluke 752.4, with wires <4 feet in length, two terminal connection is adequate).
Step I Short the nullmeter terminals on the 2720 and short them to the OUTPUT
LOW terminal on the 2720 using 24AWG bus wire or similar. Turn on the
nullmeter and allow anv thermal emfs to subside. Zero the nullmeter.
8-4
Step 2 Remove the shorting wires on the nullmeter of the 2720. Select an output
voltage from the 2720 of the ten times the value and the same polarity as the
selected standard cell. Turn off the nullmeter. using teflon coated
connection wires of the gauges indicated (or similar) connect the standard cell.
divider and the 2720 as follows :
2720 OUTPUT LO to Divider Input LO 20AWG wire
2720 OUTPUT HI to Divider Input HI 20AWG wire
Cell LOW to Divider Output LO 24AWG rvire
Divider Output HI to 2720 Nullmeter HI 24AWG wire
Cell HI to 2720 Nullmeter LO 24AWG wire
Note that if a Fluke 752,{ divider is used then some of these connections are
made internal to the divider, care must be taken to ensure that the cell is
correctly connected to the divider otherwise it may be damaged, care must also
be taken to ensure that the nullmeter is of the correct polarity.
Select the AUTO NULL mode of operation on the 2720 with a division ratio of
+0.025, select for the deviation to be displayed in PPM. Note the settled value
of deviation displayed on the 2720. Turn off the nullmeter and remove the
connections to the nullmeter (be careful not to short them).
Step 3 Repeat Step 2 with the following connections (ensure that the initial voltage
value is re-entered on the 2720):
2720 ourPUT Lo to Divider Input Lo 20AwG wire (already present)
2720 ourPUT HI to Divider Input HI 20AwG wire (alreacly prescnt)
cell Low to Divider output Lo 24AwG wire (arready present)
Divider Output HI to 2720 Nullmeter LO 24AWG wire
Cell HI to 2720 Nullmeter HI 24AWG wire
Select the AUTO NULL mode of operation on the 2'720 wlth a division ratio of'
-0.025 (NOTE POLARITY). Note the settled value of deviation clisplayed on
the 2720. Turn off the nullmeter and remove the connections to the nullmeter
(be careful not to short them).
Step 4 Repeat steps 2 and 3 for each cell in the cell bank (the user may make as
many measurements as wished), separately noting each ppm deviation of the
2720.
Step 5 Calculate the mathematical average of all of the ppm deviations recorded for
the steps 2 and 3, i.e. add up all of the deviations and divide the result by
the number of measurements taken. THIS DEVIATION IS THE ERROR oF TIIE
IO VOLT RANGE OF THE 2720 AND MAY BE RECORDED IN THE
CALIBRATION RECORD OF Tr{E 2720 IF DESIRED (NEGATIVE RESULT
INDICATES THAT THE 2720 OUTPUT IS HIGHER THAN EXPECTED). Note
this calculated ppm deviation (be careful to record the polarity of the error.
If desired the standard deviation of the data may also be calculated (this gives
an indication of the random error in the measurement). THE USER MAy
ALSO NOTE THAT INTER-CELL COMPARISONS MAY BE ACHIEVED AT TI.tE
SAME TIME, THE AVERAGE OF EACH CELL'S STEP 2 AND 3 DEVIATION
MAY BE INTER-COMPARED YIELDING THE ACTUAL PPM DEVIATION FROI\4
CELL TO CELL.
Step 6 Remove all connections from the 2720. divider and the standard cell bank.
8-5
Step 7 Select an output from the 2720 of +10.0000000 V then enter the ppm deviation
obtained in step 5 (ensure that the same polarity is used). The 2720 output
voltage is thus set to EXACTLY 10.0000000 V. The worst case error in the
2720 output is 0.25ppm (typically < 0.lppm)'
Step 8 Connect the 27 20 to the 2734A as follows using 24AWG wires :
2734A COMMON tO 2720 OUTPUT LOW
2720 OUTPUT HI to 2720 NULLMETER HI
2734A r}Y to 2720 NULLMETER LOW
Select the AUTO NULL mode of operation on the 2720 with a division ratio of
+0.25, select for the deviation to be displayed in PPM' Note the settled value
of deviation displayed on the 2720. Turn off the nullmeter and remove the
connections to the nullmeter (be careful not to short them)'
Step 9 Repeat Steps 7 and 8 with the following connections (ensure that the value is
re-entered on the 2720):
2734A COMMON to 2720 OIJTPUT LOW (should be already present)
2720 OIJTPUT HI tO 2720 NULLMETER LO
2134A t}V to 2720 NULLMETER HI
Select the AUTO NULL mode of operation on the 2720 with a division ratio of
-0.25 (NOTE POLARITY). Note the settled value of deviation displayed on the
2720. Turn off the nullmeter and remove all connections.
Step 10 Compute the average of the two deviations recorded in steps 8 and 9. This
value is the ppm deviation of the lOV output of the 2'734A from the nominal
value, a negative value indicates that the 2734A actual output voltage is lorver
than nominal.
Using the above procedure the worst case error is 0.5ppm, however due to averaging of
measurements and the procedure used the nominal error (RMS of errors) is less than
0.3ppm worst case and typically less than 0.lppm (plus the traceability error of the
standard cells and the error of the divider).
8.5.4 Measurement of the V7 Output Voltage
This measurement follows the same procedure as shown for the l0V output in paragraph
8.5.3 above, howeVer a voltage of 7.0000000 V is used in steps 7,8 and 9, and the error
is increased (due to the slightly extended range over which the linearity of the 2720 is
used) by 0.2ppm worst case. Note that if the l0V output was measured immediately
preceding this measurement then steps I through 6 are unnecessary, the data calculated
in step 5 of 8.5.3 being re-used.
8.5.5 Recording and Analyzing Data
As shown in Table 8-1, the deviations of the l.0l8V (A), l.0V (B), lOV (C) and V7 (D)
outputs and the differences between the deviations of the l.0l8V andYT (E), l.0V and
VZ (F), and the Y7 and lOV (G) outputs should be recorded.
i) Ifdata (E), (F) and (G) are similar then the measurement of the V2 output is
suspect and should be repeated.
8-6
ii) If data (E) and (F) are similar, but not similar to data (G) then the measurements
of the l0V and V2 outputs are suspect (possibly the standardization of the 2720 or
the divider itself could be suspect) and should be repeated.
iii) If data (A) and (B) are similar to previous measurements but measurements (C)
and/or (D) are not, then all measurements are suspect and should be repeated.
iv) Any change in data (D) should also reflect in changes of data (A), (B) and (C). If
this is not the case then all measurements are suspect and should be repeated.
8.6 l\Ieasurement of Actual Output Voltages and Inter-Cell Comparison Without Adjustment.
This paragraph describes the prefered method by which "Inter-Cell" comparison is
performed within the 2734A. This comparison is normally followed by the normal
measurement of the actual output voltage values of the 2734A, this was described in
paragraph 8.5 above, thus is not described in this paragraph.
Equiprnent Required : Valhalla 2720G5 or HSR
Step 1 Remove the CALIBRATION AccESS CovER from the 2124A (see paragraph 8.2).
Select all functional references to be in use (all switches down). If it has
been previously determined that one reference is faulty then it may be deletecl
(switch up).
Step 2 Short the nullmeter terminals on the 2720 and short them to the OUTpUT
LOW terminal on the 2720 using 24AWG bus wire or similar. Turn on the
nullmeter and allow anv thermal emfs to subside. Zero lhe nullmeter then
turn it off.
Step 3 Remove all connections from the 2720 nullmeter. Set the 2720 output voltage
to 7.0000000 v and provide the following connecrions using 24AwG teflon
coated wire (or similar) :
2720 OUTPUT LOW to 2734A COMMON
2720 OUTPUT HI to 2720 NIJLLMETER HI
2734A Y7 to 2720 NULLMETER LOW
Select AUTO NULL mode on the 2720 with a division ratio of +0.25 and select
for the deviation to be displayed in PPM. After settling deselect Auro NUt.t.
Step 4 Turn oN the nullmeter, the deviation display should show approximately zero
PPM (within 3ppm is sufficient).
Step 5 Turn off all but one reference cell in the 2734A (i.e. all swirches but one
should be up). NEVER DESELECT ALL CELLS OF THE 2134A. After tne 2720
nullmeter has settled, note the displayed deviation.
Step 6 Repeat step 5 for each reference in turn (select the next reference then
deselect the previous) until measurements have been made and noted for all
four references.
8-7
Step 7 If the difference between the smallest (i.e. most negative) deviation and the
largest (i,e. most positive) deviation is greater than 30ppm then realignment of
the references is required and the procedure in paragraph 8.7 should be
followed.
Step 8 Repeat step 5 for each possible pair of references (i.e. l+2, l+3, l+4, 2+3,2+4.
3+4). Check that the measurements obtained are within 0.5ppm of the average
of the two individual measurements obtained in step 5. If any measuremenr
fails then repeat each individual measurement and re-check. if this still fails
then the 2734A is faulty and should be repaired.
Step Select all four references and replace the CALIBRATION ACCESS covER.
Step 10 Compute and record on a form similar to that shown in table 8-2 the actual
measured deviations in steps 5, 6 and 8 (data [A] through [J]), the average of
the deviations measured in step 8 (data [K]), and the actual measured deviation
for each reference (steps 5 and 6) minus the average deviation from step 8
(data [L] through [O]).
Step 11 After 5 minutes stabilization, perform the measurements of paragraph 8.5
above.
8.6.1 Analysis of Results
Data [L] through [O] represent the ppm deviation of each individual cell from the
average of all four references, thus (given singular major events) it is possible to
immediately note changes in the value of a single reference cell and compute its affect
on the average. This is seen by one cell having a large change in deviation (DeltaD) and
the other three having a smaller change in deviation of the opposite polarity (change
should be l/3 of DeltaD approximately), this indicates that the particular cell has
changed its value by 4*DeltaD/3 ppm and thus the average will have been altered by
DeltaD/3 ppm. This can be checked (if available) against any change in the actual
voltage of the V2 output, any remaining change being caused by shifts in the other three
cells.
8.7 Adjustment of output voltages and./or Realignment of Reference Cells.
This procedure basicatly follows the same procedure as shown in 8.5 and 8.6 above,
however the user adjusts the errors to be as small as desired. When making adjustments
of the potentiometers in the 2734A it is important that they be made in the correct
order, as each adjustment has an affect on the others. The outputs which are affected
by each adjustment are as follows :
i) Cell adjustment Affects all output voltages by 0.25 times adjustment made.
ii) l.0V adjustment Affects l0V output by 0.05 times adjustment made.
iii) l.0l8V adjustment Affects l0V output by 0.05 times adjustment made.
iv) l0V adjustment Has no affect on other output voltages.
8-8
8.7.1 Adjustment of Individual Reference Cells
This procedure adjusts each cell to be nominally 7.000V and to be within +/- 5ppm of the
average value. Note that all other adjustments and/or measurements must be made
following adjusting any of the REF l, REF 2, REF 3 or REF 4 adiustments.
Step Follow the procedure in 8.5.3 steps I through 6 (i.e. standardize the 2720).
Step Select an output of 7.0000000 v from the 2i20 and connect the 2720 to rhe
2'734A as follows using 24AWG teflon coated wire (or similar) :
2734A COMMON to 2720 OUTPUT LOw
2720 OUTPUT HI to 2720 NULLMETER LO
2734A Y7 tO 2720 NULLMETER HI
Turn on the nullmeter on the 2720 and select for the deviation display to be
in PPM. For each reference cell in turn being singularly selected (only one
switch down) adjust the respective "REF N" potentiometer for a nullmeter
indication of < +/'5ppm. Turn off the nullmeter, remove all connections ancl
reselect all references.
8.7.2 Adjusting the 1.0V Output
Note that the l0V output adjustment and/or measurement may have to be remade
following adjusting the l.0V output.
Step Follow the procedure in 8.5.1 steps I through 6 (i.e. standardize the 2720).
Step Select an output of 1.00000000 v from the 2i20 and connect the 2120 to the
2734A as follows using 24AWG teflon coated wire (or similar) :
2734A COMMON to 2720 OUTPUT LOW
2720 OUTPUT HI to 2720 NULLMETER LO
2734A t.0V to 2720 NULLMETER HI
Turn on the nullmeter on the 2120 and select for the deviation display to be
in PPM. Adjust the l.0V potentiometer for a minimum nullmeter reading
(within the limits required by the user). Turn off the nullmeter and remove
all connections.
8.7.3 Adjusting the 1.018V Output
Note that the l0V output adjustment and/or measurement may have to be remade
following adjusting the t.0l8V output.
Step I Follow the procedure in 8.5.1 steps I through 6 (i.e. standardize the 2720).
This step is unnecessary if the l.0V adjustment was made immediately prior to
making this adjustment.
Step 2 Select an outputof 1.01800000 V from the 2720 and connect the 2120 ro rhe
2734A as follows using 24AWG teflon coated wire (or similar) :
2734A COMMON to 2720 OUTPUT LOw
2720 OUTPUT HI to 2720 NULLMETER LO
2734A l.0l8v to 2720 NULLMETER HI
Turn on the nullmeter on the 2720 and select for the deviation display to be
in PPM. Adjust the l.0l8V potentiometer for a minimum nullmeter reading
8-9
(within the limits required by the user). Turn off the nullmeter and remove
all connections.
8.7.4 Adjusting the 10V Output
Step 1 Follow the procedure in 8.5.3 steps I through 6 (i.e. standardize the 2720).
Note that if the reference cell adjustment (8.7.1) was made immediately prior
to this adjustment then this step is unnecessary.
Step 2 Select an output of 10.0000000 V from the 2720 and connect the 2720 to the
2734A as follows using 24AWG teflon coated wire (or similar) :
2734A COMMON to 2720 OUTPUT LOW
2720 OTJTPUT HI to 2720 NULLMETER LO
2134A IOY tO 2720 NULLMETER HI
Turn on the nullmeter on the 2720 and select for the deviation display to be
in PPM. Adjust the l0V potentiometer for a minimum nullmeter reading
(within the limits required by the user). Turn off the nullmeter and remove
all connections.
8.7.5 Post-Adjustment Procedure
After making any adjustment to the 2734A it is recommended that the measurement
procedure be followed in full (paragraph 8.5) to check that the adjustments have been
correctly made. The user should note that the CALIBRATION ACCESS COVER should be
in place during these measurements.
8.8 Internal Link Selection
After some period of time, or following component replacement, it may become necessarl,
to re-center one or more of the adjustment potentiometers. This is achieved by means
of binary weighted links behind each adjustment. These links can be accessed by
removing the front upper bezel, followed by removing the top cover, followed by
removing the top cover of the Reference Enclosure. Each link pattern is immediately
behind its respective adjustment potentiometer and is orientated such that the link with
the smallest effect is towards the front of the 2734A, each link further back having
almost twice the effect of the previous link.
8- l0
SECTION IX - MAINTENANCE AND TROUBLESHOOTING
9.1 General
The following paragraphs provide the information required to perform the required
periodic maintenance and basic guidelines for troubleshooting the 2734A.
9.2 Periodic Maintenance
The 2734A requires little periodic maintenance, that which is required is discussed in the
following paragraphs.
9.2.1 Cleaning
It is recommended that the 2734A be operated in a clean environment, however, if the
environment is "dusty" then periodic cleaning of the unit will be required.
Loose dirt or dust, which is collected on the exterior surfaces of the 2734A may be
removed with a soft cloth or brush. Any remaining dirt may be removed with a soft
cloth dampened in a mild soap and water solution. Do not use abrasive cleaners.
The front panel may be cleaned with a soft cloth and a "Windex" type cleaner. Do not
use petroleum based cleaners on the front panel.
If required, the 2734A interior may be cleaned by blowing with dry compressed air.
If the 2734A has become "heavily" contaminated with dirt or by other contaminant(s)
then it is recommended that the unit be completely overhauled (contact your local
Valhalla Scientific Service Center for details).
9.3 Troubleshooting
The following paragraphs give basic procedures for troubleshooting and