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HEWLETT
PACKARD
SERVICE INFORMATION FROM H E W L I I =PAGKARD
~
1st Quarter 1998
David B. Grant /Hewlett-Packard The adapters that were shipped on the Caution
instrument can be removed from the These cleaning processes apply only
Proper cleaning and handling of connectors on the instrument. If you re- when dry connections are used
lightwave connectors is imperative for move these adapters you should keep (no index matching compounds).
achieving accurate and repeatable mea- the exposed connector of your instru- Hewlett-Packardstrongly recommends
surements with your Hewlett-Packard ment covered until the next use. against the use of index matching com-
lightwave equipment. Lightwave inter- Protective covers for these exposed pounds, particularly gels, as they may
faces should be cleaned before each connectors are not provided with the be difficult to remove and can contain
measurement using the techniques de- instruments, so it is best to keep the damaging particulates. If an index
scribed here. Information on protecting adapters on the instrument with the matching compound is used, contact
and storing your connectors/cables, dust covers on. the compound manufacturer for spe-
and tips on how to properly mate con- cific information about recommended
nectors are also included. Making Connections solvents and cleaning procedures.
When you insert the ferrule into a con-
Handling nector or adapter, make sure that the Cleaning Non-Lensed
Always handle lightwave connectors fiber end does not touch the outside of Lightwave Connectors
and cable ends with great care. Fiber the mating connector or adapter. In this
ends should never be allowed to touch way, you will not rub the fiber end Equipment
anything except other mating surfaces against any undesirable surface. Many The following is a list of the items that
or cleaning solutions and tools. connectors have a keyed slot provided should be used to clean non-lensed
for optimum measurement repeatabil- lightwave connectors.
Caution ity that also helps to align and seat the
Hewlett-Packard strongly recommends two connectors. After the ferrule is
that index matching compounds not be
applied to HP instruments and acces-
properly seated inside the other con-
nector, use one hand to keep it straight,
71 Description
Isopropyl alcohol
HP Part No.
8500-5344
sories. Some compounds, such as gels, rotate it to align the key, and tighten it Cotton swabs 8520-0023
may be difficult to remove and can con- with the other hand. Compressed air 8500-5262
L
tain damaging particulates. If you think
the use of such compounds is necessary, Most connectors using springs to push Caution
refer to the compound manufacturer fiber ends together exert one to two Hewlett-Packard recommends that you
for information on application and pounds of force. Over-tightening or un- do not use any type of foam swab to
cleaning procedures. der-tightening these connectors can clean optical fiber ends. Foam swabs
result in misahgnment and non-repeat- can leave filmy deposits on fiber ends
Storage able measurements. Always finger that can degrade performance.
tighten the connector in a consistentman-
All of Hewlett-Packard's lightwave in- ner. Refer to the manufacturer's data
struments are shipped with either laser Process
sheet for any torque recommendations. Before cleaning the fiber end, clean the
shutter caps or dust caps on the
lightwave adapters that come with the ferrules and other parts of the connec-
instrument. Also, all of the cables that Cleaning tor. Use isopropyl alcohol, clean cotton
are shipped have covers to protect the Two cleaning processes are provided. swabs, and clean compressed air. Then
cable ends from damage or contamina- The first process describeshow to clean use alcohol to clean the fiber end. Some
tion. These dust caps and protective non-lensed lightwave connectors. The amount of wiping or mild scrubbing of
covers should be kept on the equip- second process describes how to clean the fiber end can help remove particles
ment at all times except when in use. lightwave adapters. (See "Measurement Information,"page 4)
Pub. NO. 5964-6006E 0 Hewlett-Packard 1998
WWW.HPARCHIVE.COM
0.015 n lead resistance
+
+s .
Power Supply
Programmed 5.3 V
for 5 V . 10A
-s .
I
Load leads are
6 f o o t AWG 14
Remote sensing can correct the load-lead
problem.
To implement remote sensing, discon-
nect the local sense leads from the out-
put terminals. Use twisted two-wire
shielded cable to connect the power
supply sensing terminals to the sense
points on the load. Don't use the shield
as one of the sensing conductors. Con-
nect one end of the shield to ground
and leave the other end unconnected.
Sensing currents are typically less than
lOmA, and as a general rule, you
should keep the voltage drop in the
sense leads to less than 20 times the
power supply temperature coefficient
(usually stated inmV/"C). This is easy
to achieve with readily available
. .. shielded two-wire cable.
Tip *Z. Eliminate Noise from
9
Bench, system and rack-mount power the higher the wire gauge, the worse
supplies are frequentlyused in test and the regulation gets. Compare output Low-level Measurements
measurement (T&M) environments, in- impedance of a well-regulated 10A
cluding automatic test equipment supply, which might have an output Noise in low-level measurements can
(ATE) systems. This article adapted impedance of 0.2 milliohms, with the come from a number of different
from material contributed by Hewlett- resistance of copper wire: sources and it's easier to eliminate
Packard (Canada) Ltd., Mississauga, noise than to filter it. Check these noise
ON, provides practical tips on how to sources.
best use power supplies in a number H Power supply: starting with a low-
of common scenarios. noise supply is naturally a great way
to keep noise out of your measure-
ments. Linear power supplies have
Tip #1. Remote Sensing Com- lower common-mode noise currents,
pensates for Load-lead Effects and operate at low frequency. How-
When your power supply leaves the ever, you can use switch-mode sup-
factory, its regulation sense terminals plies successfully if their specifica-
are usually connected to the output ter- tions include a low common-mode
minals. This limits the supply's voltage Regulation gets even worse if you use current. As a rule of thumb, com-
regulation abilities, even with very a relay to connect power to the load. mon-mode current over 20 to 30mA
short leads. The longer the leads and is likely to cause trouble.
Remote sensing, in which you connect w DUT-to-power-supply connections:
the sense terminals of the power minimize conducted noise by elimi-
supply's internal feedback amplifier nating ground loops. Ideally, there
P o w r supply 't
+S
directly to the load, lets the power sup- should be only one connection to
Programmed -s Load @ V ply regulate its output at the load ter- ground. In rack systems, where mul-
for 5 v. 10 A
minals, rather than at its own output tiple ground points are inevitable,
terminals. The supply voltage shifts as separate the dc distribution path
necessary to compensate for the resis- from other conductive paths that
tance of the load leads, relays, or con- carry ground currents. If necessary,
Effects of six feet of AWG14-gauge leads nectors, thereby keeping the voltage at float the power supply: don't connect
without remote sensing. the load constant. either terminal directly to ground.
2 BENCH BRIEFS 1 ST OUARTER 1998
WWW.HPARCHIVE.COM
t r path for noisy ground loop cur-
un I
rent at higher frequencies.To balance
the DUTs impedance to ground for
your test frequencies, use a common-
mode choke in series with the out-
put leads and a shunt capacitor from
each lead to ground.
Use twisted shield leads for both output
and remote sense leads to minimize radi- m Current variation to the DUT rapid
ated pick-up. changes in the DUT's current de-
mand cause voltage spikes. To pre-
Minimize electrical and magnetic ra- vent this, add a bypass capacitor This HP VEE program makes parametric
diated pick-up by using twisted close to the load. The capacitor measurementsand captures the pulse cur-
shielded conductors for the output should have a low impedance at the rent loading of a digital cellular phone.
and remote sense leads. To make sure highest testing frequencies. Avoid
the shield doesn't carry current, con- imbalances in load lead inductance; need to evaluate both the peak and dc
nect the shield to ground at one end direct connections to the DUT, such averages current draws. You could use
only, preferably the single-point as twisted shielded pair, are your an oscilloscope to monitor a shunt or a
ground on the supply. best bet. current probe, but this approach raises
Minimize the power supply's com- issues with voltage drops, ground
mon-mode noise current by equaliz- Tip #3. Use Your Power Sup- loops, common mode noise, space, and
ing the impedance to ground from calibration.
plv to Measure Pulsed Current
the plus and minus output terminals.
Also equalize the DUT's impedance To adequately specify the power source As a simpler and cheaper alternative,
to ground from the plus and minus for products that exhibit pulsed and use a power supply with built-in mea-
input terminals. Magnetic coupling dynamic current loading, such as digi- surement capabilities. HI' 66312A and
or capacitive leakage provide a re- tal cellular phones and hard drives, you 66332A dynamic measurement dc
sources store up to 4.096 data points at
sample intervals from 15.6ms to
DC Supplies Give Instant 31,200s. Like an oscilloscope, they ac-
Peak Measurements quire pre and post-trigger buffer data
HP 66312A (40W) and 66332A (1OOW) by crossing a user-set threshold.
power supplies provide instantaneouspeak
measurement capability; users no longer You can use SCPI commands in the Set
need scopes or high-speed digital voltme- Up Source, Measure, and Enter Array
ters to test devices that draw pulsed current. blocks. You can use these commands
Specifications include: Dynamic current measurements accu- in other programming environments as
Precision current measurement as low rate to 0.6% + 1mA (66312A). well. Note that MEAS can be used in
as 0.6pA. Voltage output: 0 to 20Vdc. place of FETC to cause an immediate
Dynamic voltage measurements accu- Current output: 0 to 2Adc (66312A), 0 to trigger. Obtain subsequent measure-
rate to 0.03% + 5mV. 5 A (66332A). ment parameters from the same data
by using FETC. 0
the life of a product and are impera- You no longer have to order the entire
hsarurnenff. S e w i c e tive for customers that service their service note index (in excess of 30
own HP products. pages), but can select a custom index
Notes For 9 P Trade of model numbers of your choice.
New FAX Service
Customers A new fax service has been imple- New WEB Service
mented with a new phone number. T&M service notes are now available
If you are familiar with the process on the world-wide web. The url is
of obtaining service notes from the
Introduction fax system, you will like our new hp.com/ go/ tm-servicenotes
http:/ /m.
Test and Measurement (T&M)Service system. It is much easier to use.
Notes contain product-specific service T&MService Notes can be viewed and
information about Hewlett-Packard HP T&M Service Note Fax System- ordered from this site for delivery to
products. Subject include product im- (650)688-4313 the fax machine number or email ad-
provements, modifications, and proce- Enter the Password-76683 dress of your choosing. Other benefits
dures for troubleshooting, mainte- include shoppingbasket-type selection
nance, and repair. Service notes are The scripting (instructions) have of service notes, and looking at select
published as appropriate throughout changed and are more user friendly. model number indexes. 7
1ST QUARTER 1998 BENCH BRIEFS 3
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ition,"page 7)
can be done by lightwave adapters. In addition, small light is received into a lens rather than
I a cotton swab foam swabs (HP Part No. 9300-1270) into a connecting fiber. These receiving
forth across the
This technique
;place particles
may be used along with isopropyl al-
cohol and compressed air to clean the
inside of lightwave connector adapters.
lenses usually have an anti-reflective
coating that is very easily damaged.
Therefore, these connectors should
r.
n. never have cleaning solutions or any
Note: As noted in a previous caution other substance applied to them unless
D dry (about 1 statement, the foam swabs can leave it is specifically recommended by the
nediately with filmy deposits.These deposits are very manufacturer. You may wish to use
:ompressed air thin however, and the risk of other con- clean compressed air to rid them of
:posits remain- tamination buildup on the inside of dust from time to time.
3er the alcohol adapters greatly outweighs the risk of
3e blown hori- contamination of foam swab deposits Summary
ir end. Visually left from cleaning the inside of adapt- When making measurements with
or stray cotton ers. lightwave instruments or accessories,
mnector is dry, the following precautions will help to
be made. Process insure good, reliable, repeatable mea-
Clean the adapter by applying isopro- surements:
pyl alcohol to the inside of the
sed air canister connector with a foam swab. Allow the w Use extreme care in handling all
duce residue on adapter to air dry, or dry it immediately lightwave cables and connectors.
efer to instruc- with clean compressed air. w Be sure the connector interfaces are
compressed air clean before making any connec-
tions.
Cleaning Lensed Connections
/e Adapters Some instruments may have a connec- Use only the cleaning methods de-
tor that is "lensed." In other words the scribed.
ibove for clean- connection does not provide a physi- Keep connectors and cable ends cov-
? used to clean cally contacting connection, but the ered when not in use. 0
c
Bulk Rate
U.S. Postage
PAiD
Santa Clara, CA
BENCH BRIEFS
Permit No.
1st Quarter 1998
90
Volume 38 No. 1
Service information from
Hewlett-Packard Company
To obtain a qualification form for a free
subscription, send your request to the
above address.
Reader comments or technical article
contributions are welcomed.
Please send them to the
Bench Briefs Editor at the above address. f
Editor: Jim Bechtold
Hewlett-Packard
All rights reserved Permission to reprint Bench Briels granted upon wrltten request to the Edltor Printed in U.S.A
1ST QUARTER 1998
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