Does anyone (including AD) have any examples of using the AD7794 to measure different thermocouples and/or RTDs with the same circuit?
attached is a schematic showing the AD7794 connected to 2 RTDs. Four wire RTDs are used in the diagram. The AD7794 has 2 excitation currents and each excitation current is dedicated to an RTD. An external precision resistor is used to generate the reference voltage. The current flowing through the precision resistor is IOUT1 + IOUT2. The matching between IOUT1 and IOUT2 is +/-0.5% typically.
If you wish to connect more RTDs to the AD7794, the excitation currents would need to be shared between RTDs. So, some muxes would be needed to direct the excitation current to the selected RTD.
The AD7794 can directly accomodate 3 thermocouples in that channel AIN1, AIN2 and AIN3 have a bias voltage generator. This will bias the thermocouple signal so that it sits within the ADC power supply rails. To add further thermocouples, some external biasing is required. For the cold junction compensation, a thermistor could be used. Please review the application circuits in the AD7792/3 datasheet to see the connections needed.
How many RTDs/TC do you wish to connect to the AD7794?
Thanks Mary. That's kind of what I ended up doing.
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