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Topic: PT1000 RTD help please (Read 5 times) previous topic - next topic

retrolefty


Thanks Lefty - is some kind of thermal grease used to ensure good readings? I was toying with the idea of using a sensor easier (to me at least) to hook up rather than a PT1000, and packing it in with something, as a plan B really if else fails.




I never heard of anyone trying to pack a thermowell with grease. I would worry that the heat of the process might cause the grease to flow and not maintain consistance contact with the sensor. Some thermowells have small internal clips at the end of the well inside, so that when the sensor is shoved in far enough help maintain a mechanical contact between the sensor and the inside wall of the well.

Lefty

al1fch

#11
Sep 16, 2011, 12:20 am Last Edit: Sep 16, 2011, 12:27 am by al1fch Reason: 1
Quote
A lot of the issues regarding signal conditioning RTDs go away with PT1000s because of the higher resistance.

I agree EmilyJane having to deal with PT100 and PT1000
In my case and my resolution needs economical current source build around LM334 does the job for PT1000 driving.  (R1 = 330,   R2= 10*R1 = 3K3)

dc42

#12
Sep 16, 2011, 12:59 am Last Edit: Sep 16, 2011, 01:04 am by dc42 Reason: 1
What resolution are you looking for? By my calculation, if you make a potential divider using a PT1000 and a 1K resistor, and connect that directly to an Arduino analog input pin, you can measure the temperature with a resolution of 1 deg C. If you want higher resolution, you'll need an op-amp to amplify the voltage change.

Using a constant current source is all very well, but then both the current source and the ADC reference have to be stable (or the current source has to be controlled by the ADC reference). The potential divider (whether amplified or not) driven from the same voltage as is used for the ADC reference has the advantage that it is not very sensitive to changes in the ADC reference.
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EmilyJane

If you decide to not use a constant current source to power the sensor, remember that the critical component is the series resistor. For the best accuracy, it needs to be of high precision and have a low temperature coefficient with respect to temperature. Since your excitation current will be a function of the RTD resistance, accuracy will depend on knowing that the voltage drop across the series resistor varies only with that current.

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