Detecting RTD Error

[abasitparker]

Assuming I have a PT-100 connected to my RTD. How can I detect if the PT-100 itself has a short circuit or open circuit error? 

Thermocouples allow for open circuit detection. Do RTD's?

Similarly, how would I detect if a thermocouple itself had a short circuit?

Thanks

[abasitparker]

Bump. Any suggestion?

[Henrik_Volkers]

Out of range detection? 

Pt100 are specified for certain temp ranges, resulting in certain resistance ranges ...

Use two sensors and you know the difference .. three and the majority wins 🙂

[Blokk]

If you need a failsafe system, never use a single sensor. For example for heaters, you can have a sensor for control, and a second sensor for over heat detection. You also add a watchdog to your system to detect computer/controller problems, and in such case bring the system to a safe state (cut heating power).

Anyway, what Henrik wrote about expected ranges should be also applied, if your code detects out of range values, it can take appropriate actions to avoid problems and warn the user...

[GerdW]

Hi Parker,

Assuming I have a PT-100 connected to my RTD. How can I detect if the PT-100 itself has a short circuit or open circuit error? 

Please define "my RTD"!

- When I measure Pt100 with a NI9216/NI9217 I have to wire atleast 3 wires per Pt100, otherwise I get "invalid" measurement results.

- With a Pt100 a "short" or "open circuit" will result in invalid resistance values (the Pt100 is not defined for 0 Ohm or 1MOhm), so it's really easy to detect…

how would I detect if a thermocouple itself had a short circuit?

You would only measure the temperature of the cold junction…

[Henrik_Volkers · Accepted solution]

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@GerdW wrote:
[...]

how would I detect if a thermocouple itself had a short circuit?

You would only measure the temperature of the cold junction…

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If the short is at the CJ (or after the maybe external CJ) you measure ~0V and the CJ compensation will result in the CJ temperature. However if the short cut is somewhere in the TC wire, the temperature at the short will be measured (assuming a ~0 Ohm short, in case of a current leak it could be any value between temperature at the leaking point and the intended TC sensing point temp. )

Always keep in mind that the TC wires create the voltage (integral of delta temp along delta length multiplied with the Seebeck coefficient, which is a function to material and temperature)   , not the junctions , the junctions just define the start and end points of the integral.