Using a PT1000 2-wire on NI-9216

[c1Ron]

The NI-9216 is for PT100 elements, with a range of 0-400 Ohms - compatible with 3 or 4-wire connections.

How can you adapt a circuit to allow for PT1000 elements with a 2-wire connection ?

As I understand, assuming a PT100 element, you can implement jumpers to adapt for a 2-wire configuration - connecting the negative excitation pin to the negative RTD lead and the positive excitation pin to the positive RTD lead (ref Taking Temperature Measurements with RTDs: How-To Guide - NI).

Furthermore, even though it is not recommended, you can also adapt for using PT1000 element on the NI-9216 and PT100 elements on the NI-9226 (ref Temperature Measurement with Pt100 and Pt1000 - NI). The article says "you need to shift the measurement up or down using either a voltage divider or a voltage amplifying circuit".

I'm not sure how the internal circuitry of the NI-9216 is built (as I cannot find proper documentation for the device online), but as I understand, a constant current of 1mA is exciting the RTD and the voltage across the element is measured. If this is true, then the PT1000 element, due to high resistance, will yield a voltage drop that is to high - saturating the ADC ? Hence, you need to implement a resistor in parallel with the RTD such that less current flows through it ?

The figure is meant to show one channel of the NI-9216, and the external RTD with a resistor in parallel.

[GerdW · Accepted solution]

Hi Ron,

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@c1Ron wrote:

The NI-9216 is for PT100 elements, with a range of 0-400 Ohms - compatible with 3 or 4-wire connections.

How can you adapt a circuit to allow for PT1000 elements with a 2-wire connection ?

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In general the basic eletrical rules of Kirchhoff and Ohm apply here!

So the simplest solution would be to connect 10 Pt1000 sensors in parallel to the same channel of your NI9216-Pt100 module…

(Or you just buy a Pt100 sensor and use that instead of the Pt1000 type. Will cost you about 50€ for a industrial grade sensor with no additional work needed.)

When using 2-wire sensors you simply need to connect the excitation pins to your 2-wire sensor. The measurement will be a little less accurate as you don't compensate for (maybe long) the sensor wires, but only for the shorter connection from excitation to measurement pins. (I usually use a 4-wire connection cable and only do the needed connections near the sensor…)