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AIM7
Thermocouple Input Module
The AIM7 Thermocouple Input Module accepts signals The AIM7 may be placed in slots Z-10 of the system
from thermocouple tyies J, K, S, T, B, E, and Rior generic baseboard. However, to minimize power supply thermal
voltages up to L-1OOmVfull scale. The AIM7 offers 16 and noise effects, the ATM7 should be placed in the lowest
channels of differential input, as well as guard and ground numbered available slot. To install the AlM7 in a Model
screw terminals. 5OOA,5OOP, 556, remove the baseboard top cover and
or
place the module in the desired slot with the component
side facing the power supply. For the Model 570 or 575,
The AIM7 provides channel selection through on-card open the system clamshell cover and place the module in
multiplexing. Gain is fixed at 100 volts/volt. On-card cold the system option slot with the components facing up-
junction reference circuitry provides an accurate tempera- ward.
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CAUTION
Signals from the ATM7 are routed along the AN OUT signal Always turn off the data acquisition system
path to the system global amplifier and A/D converter power supply before installing or removing
where programmable gain can be applied before A/D modules. Always operate the system with the
conversion. top cover in place to minimize the possibility
of EM1 radiation.
All thermocouple inputs are applied to screw terminals
located on an isothermal block to minimize errors caused User Configured Components
by temperature differences between the input connectors
and the reference junction sensor. The cold junction refer-
ence sensor itself is mounted in the isothermal block to The signal input screw terminals located on the isothermal
accurately measure the temperature of the block. In addi- block are the only user-configured components on the
tion, a driven guard connection has been provided for the AIM7 module. For the location of these terminals, refer to
connection of signal shields. Guarding can minimize the Figure 1. Note that the terminals provide connections for
noise picked up by signal input lines. the 16 input channels as well as separate connections for
ground and guard.
Document Number: 500-917-01 Rev. D AlM7-1
TJaermocouple
Input Module
,Q@
-- ------ ---------__
PI74
`igure 1. AIM7 Module Configurafion
Table 1. Thermocouple Color Codes
Connecting Terminals
The AlM7 accepts up to 16 differential input channels. Type Material (+) Wire t-1 Wire
These channels are marked channel 0 through channel 15.
Each channel has two input terminals labeled (+>and (-1for B Platinum 30% rhodium Gray Red
positive and negative inputs, respectively. Note that you Platinum 6% rhodium
must observe proper polarity when connecting thermo- Chromel-constantan Purple Red
couples to the AlM7 module. The positive thermocouple ; Iron-constantan White Red
wire must be connected to the (+> terminal, and the nega- K Chrome&alumel Yellow Red
tive thermocouple wire must be connected to the (-1termi- R Platinum 13% rhodium Black Red
nal. The negative TC wire is usually red. Typical connec- Pure platinum
tions for channel 0 are shown in Figure 2. In this example, S Platinum 10% rhodium Black Red
the shield is connected to the guard terminal; guarded con- Pure platinum
nections are discussed in the following section. r Copper-con&man Blue Red
Color coding of thermocouple wires varies according to
type. Table 1 gives the ANSI color codes for the various CAUTION
thermocouple types supported by the Module. When Maximum input voltage is 215V (power on),
adding extension cable, use only the specific type of cable or HOV (power off). Exceeding these values
recommended for the thermocouple being used. may damage the module. If any input exceeds
klOV (power on), measurement error is likely
to occur.
AlM7-2
ThermocoupleInput Module
Guarding Connecting Thermocouples
On long signal runs, or in electrically noisy environments, A thermocouple is a sensor made by joining two dissimilar
use shielded cable to reduce noise pickup. If your tempera- metals for the purpose of temperature measurement. When
ture reading is unstable, noise induced into the thermo- dissimilar metals are joined in a closed circuit, and the two
couple wire may be the problem. junctions are held at different temperatures, a small electric
current will flow through the circuit. The voltage gener-
ated under such conditions will depend on the tempera-
When using shielded thermocouples with the AlM7, the ture difference between the two junctions as well as the
shield should be connected to one of the AIM7 guard types of metals being used.
terminals rather than moduleground or baseboard ground.
These terminals are actively driven by an on-card buffer
amplifier, so that GUARD is maintained at the common When thermocouples are used for temperature measure-
mode voltage of the input signal. ment, one junction is kept at a known reference tempera-
ture (often the melting point of ice: O'C). Tables and curves
that describe the relationship of thermocouple voltage to
If the shield is connected in this manner, it should not be temperatures assume that the temperature of the reference
connected to the thermocouple signal wires or to ground at junction is 0