Keithley 2701, User Manual

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3-38 Basic DMM Operation Model 2701 User’s Manual
Connections
NOTE When using the front panel inputs, the INPUTS switch must be in the “F” (out)
position. For switching modules, it must be in the “R” (in) position.
Thermocouple connections
Connections for thermocouples are shown in Figure 3-14. Thermocouples are color coded
to identify the positive (+) and negative (-) leads (Table 3-2). Note that the negative (-)
lead for U.S. type T/Cs is red.
For front panel inputs, you need to use a simulated reference junction for thermocouple
temperature measurements. An ice bath, as shown in Figure 3-14A, serves as an excellent
cold junction since it is relatively easy to hold the temperature to 0°C. Notice that copper
wires are used to connect the thermocouple to the Model 2701 input.
NOTE The positive lead of the type T thermocouple is made of copper. Therefore, that
lead can be connected directly to the input of the Model 7700. It does not have to
be maintained at the simulated reference temperature (i.e., immersed in ice
bath).
For the Model 7700 switching module, you can also use a simulated reference junction as
shown in Figure 3-14B or you can connect the thermocouple wires directly to the screw
terminals (internal reference junction) as shown in Figure 3-14C. Using a simulated
reference junction may be inconvenient but it will provide more accurate temperature
measurements (assuming the user enters a precise reference temperature).
With open thermocouple detection disabled, the Model 2701 can calculate the average
temperature of two thermocouple channels using Channel Average (see Section 5 for
details). As shown in Figure 3-14D, one thermocouple is connected to a primary channel
(1 through 10), and the other thermocouple is connected to its paired channel (11 through
20). Channel 1 is paired to channel 11, channel 2 is paired to channel 12, and so on. Keep
in mind that a simulated reference junction (i.e. ice bath) can instead be used for these
thermocouple temperature measurements.
2701-900-01.book Page 38 Wednesday, August 3, 2011 9:43 AM