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Five PT100 probes with CR1000

LoggerSupportNeeded Aug 31, 2020 09:35 AM


I asked for assitance on a nine year old thread for this exact situation but have received no response.

The shortcut wizard cannot produce a program for more than 3 "three-wire half-bridge" probes.  Why is this?

I am looking for a program that produces data tables that outputs the resistance of the probes.  I will do the temperature conversion myself in a spreadsheet for better accuracy.

My circuit consists of a 3-wire half-bridge with a 3-wire Pt100 probe (99.9ohm @ 0°Celcius) and my fixed resistor is 10kohm.

Can someone help me out by providing a program or some advice?

Using the same excitation channel for multiple probes is acceptable but I also have access to a CR800 and a 16/32B multiplexer if that makes things easier.  Any help is appreciated.

email: nick_hopey@hotmail.ca



*EDIT*   I just realized the probes do need to be in series instead of parallel so the current is not split which will throw the readings off.

aks Sep 1, 2020 11:28 AM

My guess is the Short Cut limits it to three  sensors, because there are only three excitation channels. If you can accept multiple sensors excited by same excitation channels then you can connect upto 7 Pt100 maximum. All sensors will be in series and if any part of the circut goes down, all your measurements will be in trouble. If you need only 5 Pt100, then we can put two of them together excited by one channel. I will send you a wiring diagram and a sample program in e mail a little later today.

16/32B multiplexer would certainly make it easier, but may not be needed for just five temperatur probes. 



LoggerSupportNeeded Sep 1, 2020 12:44 PM

Hi Aks,

I appreciate the reply.  Why 7 Pt100 maxium?  Because of current limitations for I/O?

From my understanding, if I used the same excitation channel for multiple probes, the only thing that would be in series is the 10k resistor, which the excitation voltage is supplied thru.  If this resistor were to die, then yes, all of the probes on this channel would no longer function.

The Pt100 probes would all be in parellel after the fixed resistor and would each be on their own differential channel.  If the fixed 10kohm resistor were to die, then yes, all of the probes on this channel would no longer function. Correct?

I have a diagram but I can't find a way to post an attachment here.

I look forward to the diagram/code.



aks Sep 1, 2020 03:21 PM

I was thinking of measuring current in the circuit more accurately using one differential channel, to improve the temperature accuracy. But if all you want is 3Wire measurement, you can connect eight probes. If you can live with two wire measurements, you can connect even more. I sent you a diagram and program already for five Pt100.

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