Can someone advise me whether there is anything which can be used to convert the 3 wired signal from an rtd into a 2 wire input into a foxboro I/A analogue input card?

The foxboro system was purchased before a started and there wasn't a dedicated rtd card purchased. Just wondering whether I can get round this little mess.

Hope someone can help.

Thanks

 

Can I assume that a 2 wire analog input is a conventional 4-20mA analog input?

If so, you need to look for a 2 wire, loop powered "temperature transmitter" that handles an RTD input (some models are thermocouple only input). There are hundreds of manufacturers of such.

The transmitter will need its output range configured; where 4mA represents some low temperature and 20mA represents some high temperature, for instance, 0-200°C.

Some are configured at the factory. Some use a manufacturer's software and cable (which might cost more than the transmitter). High end transmitter models can be field configured with HART, which requires an expensive handheld communicator.

Most people who have a DCS also have a handheld HART communicator, but check with your instrument guy first. If not, get a transmitter that is factory configured for your range or have your local vendor range it for you.

 

An RTD is just a variable resistor. Ohm's law would solve your problem.

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Bob