MikeMl
Thanks, I like the idea, the 7016 is not the only option. could you please draw a circuit of the suggestet application?
Thanx.
Here is the basis for putting the PT100 into a bridge whose output can be read directly using a +-200mV digital DC voltmeter, either panel-mounted, or using a DMM, like my Fluke75.
I used the data shown on
this page to model the resistance variation of the PT100.
You need a very precise voltage reference of 10.00V. I would suggest the
LM4040. The three resistors R2, R3, R4 must be precision metal film resistors. To get the values specified, I would make up those values by adding up to three 1% standard value resistors in series.
In the simulation, I optimized the values of R2, R3, R4 to get the smallest Error E2 from an ideal output V2. Note the use of LTSpice as a "calculator" to compute the error between the actual circuit and an ideal circuit. Note that I minimized the error over the entire range of 0 to 300degC. If you only need to read a subset of this range, the error could be minimized over just that range, making a much better fit over then narrower range.
The difference Diff E1 between the + and - output from the bridge is where the output would normally be taken. For example, if I wanted to use my Fluke DMM to read temperature using this circuit, I would connect the leads across + and -, and set the meter to read 200mV full scale. To get the actual temperature in degC, I would multiply the DMM reading by 1000(i.e. ignore the millivolts), and then add 100. A reading of 100mV would be 200degC.
Note that in interfacing the differential output from this circuit to a panel mounted digital voltmeter, you might run into the issue that on some of the DPMs, their inputs cannot be referenced to their own supply voltage, which means you may require two power supplies which are isolated from each other; one to power the bridge, the other to power the DPM.