VTI Instruments Corp.
94 Basic EX1200 DMM Operation
provided by the EX1200 series terminal blocks provide less accuracy than a fixed reference, it
does provide the advantage of requiring no external wiring and simplifying test setup. Note that
the fixed reference is supported using the EX1200 DMM. To use external reference, the scanner
driver must be used.
Connecting to the DMM
Any thermocouple can be connected to the front panel terminals of the DMM using suitable
connectors. Though this method is not preferred in fixed installation, this can be used to quickly
make readings, and troubleshoot field wiring.
FIGURE 4-14: DMM/THERMOCOUPLE CONNECTIONS
Programming Interface
The VTEX DMM, and VTEX Scanner drivers provide the access to the features of EX1200
DMM. Refer to the below functions of the driver in its documentation.
IVTEXDmmTemperature Interface
IVTEXDmmTemperature..::.Thermocouple Property
Using an RTD
RTDs are resistance-based passive transducers where the output resistance varies with changes in
temperature. This non-linear relationship is characterized, resulting in the standardization of
RTDs. As such, the EX1200 supports several types of RTDs, allowing for the automatic
conversion of resistance readings to temperature values. RTDs supported include: PT100 (default),
D100, F100, PT385, and PT3916.
Custom RTDs are supported as well. Simply input the R
0
(nominal resistance at 0°C temperature),
α (alpha), β (beta), δ (delta) characteristics for the RTDs being used. The DMM can measure
RTDs with R
0
values between 49 Ω to 2.1 kΩ. R
0
is typically the numeric value of the RTDs name
(for example, a PT100 RTD has an R
0
of 100 Ω, a PT385 has an R
0
of 385 Ω).
The temperature-resistance correlation for an RTD is calculated using the Callendar-Van Dusen
equations. Two equations are used: one for temperatures between -200 °C and 0 °C and one for
between 0 °C and 630 °C.
For T < 0°C:
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