RTd & PlC connection

[mandarmg2912]

I'm an aspiring instrumentation engineer. I need to connect following to the PLC Micrologix 1100

RTD "PT100"
the input module is AI 0-10v
can I use instrumentation amplifier to amplify the signal of Wheatstone's bridge as signal converter?
What values of registers should be used in bridge?
Application temp. range is 0 to 200 deg. C max

As the project is part of course, its not allowed to use special I/O cards, so i've to stick with signal converter

 

[widelto]

It's better and easier if you use an RTD to 0-10 VDC converter.

 

[danw]

An RTD is a resistor with a positive temperature coefficient, so its resistance increases as the temperature increases.

An RTD is used as a sensor by supplying a stable, constant current (generally 1mA or less) and reading the voltage drop across the resistor and, generally, compensating for the lead wire resistance.

If you choose to ignore the lead wire resistance compensation, you still need to generate a constant current in order to get a voltage that is readable.

In the real world, there are two choices.

1) Use an RTD transmitter, a commercial instrument which connects to the RTD on one side and to a 'receiver' (an PLC analog input card) on the other side.

The RTD transmitter generates the excitation current, accounts for non-linearities in the RTD response, and outputs a linear signal scaled according to its configuration.

2) Use an RTD input card or universal input card that can handle direct connection of an RTD.

 

[danw]

The article at the link has a schematic for constant current source and an amplifier for an RTD.

http://dev.emcelettronica.com/howto-measure-rtd-resistance-temperature-detectors-over-long-distances

 

[mandarmg2912]

Thanks all of you for reply. Bt the fact is that, the project is not industrial grade one. Its just part of the syllabus/course for acquiring graduation in Instrumentation engineering. So it is excepted that we should use a PT 100 probe, do signal conversion/ amplification, make it in standard voltage range 0-10v & then apply it to PLC for next sequencing operation by comparing it with given setpoint. all has to be done on by students with help of any expert. A low cost system is preferred. and yes, RTD transmitter would be great solution but it is not allowed.
So, all I need is signal measurementt(as far as I know, Wheatstone's bridge is best option), & a circuit for signal amplification with output 0-10v range.

 

[shooter]

wheatstone is very good thinking, however the signal of rtd is 100 mV, so it must be amplified.
another way is to use XTR105(burr brown texas instruments) and some resistors, no need for special ones as calibration can be done in software.
it converts any signal to 4..20 mA. with one resistor of 500 ohms this can be used to input in analog port.

 

[Narlin]

I don't quite understand the issue, but this has come up often. Here is a circuit that i worked out about a year ago.
https://www.circuitlab.com/circuit/bpufyr/rtd-ohms-to-mv/

If you are in an electronics course this should work for you.
narlin