OMRON RTC PID temperature module cj1w-tc

[medkhai]

I am trying to figure out what is the precision of these modules.

I need to build a precise temperature control system in which to control the temperature of 4 vessels filled with water.
Output is heaters.

I have been reading the CJ1W-TC modules specifications here
http://www.ia.omron.com/data_pdf/data_sheet/cj1w-tc_dsheet_csm1622.pdf

and would like to use either the CJ1W-TC101 or CJ1W-TC102
they are 4 loops modules which accept input RTD PT100 sensors.

In the datasheet on page 4 it says:

Indication accuracy:
Celsius: ±0.3% of PV or ±0.8ºC (whichever is larger) ±1 digit max.
Fahrenheit: ±0.3% of PV or ±1.6ºF (whichever is larger) ±1 digit max.​

What does it mean?
I know the most basic immersion circulator (e.g. Polyscience) offers a temperature stability of ±0.07˚C, so I worry the Omron module could not even get close to that as best case scenario would be ±0.8ºC

But I am not sure what Indication accuracy actually means, I mean what indicator... it doesn't have a display!

Thank you
Med

 

[mendonsy]

I wouldn't expect the TC module to be able to hold much closer than +/- 1 degree C. If you need to do better than that you should look at the E5AR temp controller.

 

[danw]

I suspect that the reason they say 'indicated accuracy' is that the card is doing the input conversion to temperature value (in whichever units), doing the control and is reporting the temperature value to the CPU. So the whatever value the CPU 'sees' is the indicated value from the card.

Comparing 0.8 Deg accuracy with 0.7 deg stability is comparing apples with oranges.

Accuracy is a comparison to an accepted 'standard', like a certified calibration source.

Stability is how little the measured value oscillates, 'moves' up or down, or jitters.

A stable process measurement can be wildly inaccurate when compared to a standard.

An accurate measurement in a mistuned/poorly tuned PID loop can swing all the place, showing gross instability. The reading can be accurate, but all over the place.

I'm not sure what the claim of "temperature stability of ±0.07˚C" means for an 'immersion circulator' because I'm not sure whether the device is something like a 'water bath' or just an agitator component. If it's a system, like a controlled water bath, it is likely its claim to hold a stable value over a period of time. But a stability claim is not a claim of how closely the temperature measurement is to an accepted standard.

On-off control, by definition, oscillates and is not a contender for "stability". The CJ1W says it does on-off or PID control. To use PID with resistive heating elements for stability you need to run "time proportional" control, sometimes called pulse width modulated control. I suspect that the parameter "Control period
1 to 99 s (one-second units)" is how a time proportional cycle time is defined. But it might be worth checking into.

Given that any modern temperature reading resolves out to at least 2 digits to the right of the decimal point, resolution is more than adequate. In my opinion, PID tuning has a far greater impact on stability than resolution.

The spec sheet does not state whether the RTD is 2 or 3 wire. 2 wire RTD's incur an uncompensated error in the lead wire resistance. Be sure to use a 3 wire RTD input.