3-36 Basic DMM Operation Model 2700 Multimeter/Switch System User’s Manual
4-wire RTDs
For 4-wire RTDs, the temperature measurement range is -200°C to 630°C (0.01°C
resolution). RTD types that are supported include D100, F100, PT385, and PT3916. A
USER type is available to modify RTD parameters, such as the resistance at 0°C. The
USER type can be enabled from the front panel, but the settings can only be changed using
remote programming.
The RTD has a metal construction (typically platinum). The resistance of the RTD
changes with change’s in temperature. The Model 2700 measures the resistance and
calculates the temperature reading. When using default RTD parameters, the resistance of
the RTD will be 100
Ω at 0°C.
Of all the temperature transducers, the RTD exhibits the most stability and linearity. The
Model 2700 performs the 4-wire measurement using offset compensated ohms. This
provides the most accurate way to measure the low resistance of the RTD.
NOTE The equations used by the Model 2700 to calculate the temperature vs.
resistance readings listed in the RTD reference tables are provided in
Appendix F.
NOTE Only one USER RTD per scan list.
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 2700 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
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