Section 5: Basic Digital Multimeter (DMM) Operation
Series 3700 System Switch/Multimeter User's Manual
5-64
3700S-900-01 Rev. C / July 2008
RTDs (Resistance Temperature Detector)
For 4-wire resistance temperature detectors (RTDs) the temperature
measurement range is -200°C to 630°C (0.01°C resolution). The Series 3700
supports 4-wire RTD types including: PT100, D100, F100, PT385, and PT3916.
A USER type is also available to modify RTD parameters, such as the
resistance at 0°C. Like the other supported 4-wire types, 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 in temperature. The Series 3700 measures the
resistance and calculates the temperature reading. When using default RTD
parameters, the resistance of the RTD will be
at 0°C.
Of all the temperature transducers, the RTD exhibits the most stability and
linearity. By default the Series 3700 performs the 4-wire measurement using
offset-compensated ohms, which provides the most accurate way to measure
the low resistance of the RTD. For faster RTD measurements when the most
accurate measurements are not required, offset-compensation may be disabled
for 3-wire or 4-wire RTD measurements.
Use of a 3-wire RTD requires a special math capability to compensate for lead
resistance on the 3rd wire. As for 3-wire RTDs, the Series 3700 supports RTD
types including: PT100, D100, F100, PT385, and PT3916. A USER type is
available to modify RTD parameters, such as the resistance at 0°C. Like the
other supported 3-wire types, the USER type can be enabled from the front
panel, but the settings can only be changed using remote programming.
3-wire RTD connections
Shown below are 3-wire RTD connections to the Series 3700. For a 3-wire RTD
capable 40-channel switching module, paired channels are used to perform the
3-wire measurement. For example, the two input leads of the RTD are
connected to a primary channel (1 through 20), while only the LO sense lead is
connected to its paired channel (21 through 40)(see Note). Channel 1 is paired
to Channel 21, Channel 2 is paired to Channel 22, and so on.
NOTE
The HI sense of the paired channels are not used (3-wire RTD).
dmm.offsetcompensation
is a common command, shared with
fourwireohms
and
drycircuit
. To enable or disable RTD offset
compensation, first select the temperature function, next the
transducer, and lastly, the offset compensation state.