Problem about using NI-9217 measure resistance

[Henrik_Volkers]

What resistor range and resolution do you need?

1mA for 100 ohm is 100mV,   the 9215 accuracy is ~8.5mV   (narrow temperature range) mmmhh  

or in other words ... do not expect a accuracy below ~8.5 Ohms ... For a PT100 RTD that is about +-22°C

and increasing the current results in more self heating ....

The open connector voltage you measure is due to the bias current of the device.

[agentchick]

How should I understand the "accuracy"? Is that the value will fluctuate in the range of 8.5ohms?

I do want to measure a kind of PT100 and the measuring current for this PT100 is about 1mA, self heating coefficient in air is 1.8 mW/°C.

[Henrik_Volkers]

Coarse spec cheeck: 7LSB peak to peak noise , 7*2*10.4V/2^16 -> 2.2mV p2p ->2.2Ohm p2p noise -> ~5.5°C p2p noise

 (a software  low pass filter will help :D)

again: What do you need?

If you have sort of a Pt100 and stuck with the 9215 look for a pt100 to 0-10V converter, thats a common industrial part.

[agentchick]

I need to measure the resistance of PT100, I need the resistance value.

[agentchick]

I made it successfully get the resistance, but with big fluctuate value. How can I decrease the noise? I have two other device, 9211, 9205

[Henrik_Volkers]

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@agentchick wrote:

I need to measure the resistance of PT100, I need the resistance value.

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OK , fine, your setup will do it 🙂

BUT can use the result??

...  with about +-8.5  Ohm uncertainty and 2.2 Ohm peak to peak noise ...  can't tell you about the drift ...

-- and the uncertainty, drift, noise of your current source will add some more ...

You told us already about the pt100 resistance measurement... boy .. it must be very hard to tell me/us your requirements ....

There are three (3) components that define a measurement:

1. a number
2. a unit
3. the uncertainty

sometimes you just need resolution and stability ... what do you need?

If you can use a hack and use the other devices .. I can't tell you unless you tell me what you need to measure...  what is the question you want to answer with your measurement?

[agentchick]

The range is from 100ohms ~ 150 ohms. 

Now the problem is to improve the stability.

I tried to increase the current to 3mA, which the measuring current of this PT100 should be 0.5mA, but the noise is still larger than 0.1 ohms.

I want to know how to make the total noise smaller than 0.1 ohms. 

[Henrik_Volkers]

As already mentioned: A low pass filter ALWAYS helps 😉