Universal Input Port- RTD, Thermonuclear, 4-20mA, 0-10V

Hi Dheeraj,

we have many different ADCs that are being used in such kind of Analog Input Modules. Finding the right ADC will depend on your exact requirements.

As Alex already mentioned, ADS124S08 is one potential ADC that is being used in such kind of modules.
If even higher performance or data rate is required, then ADS1261 would be a fit.
The ADS125H02 would be great solution which could also directly measure 10V signals.

Unfortunately we don't have collateral available yet that describes how to implement such kind of a universal input module.
But the following application notes at least explain how RTD and thermocouple measurements could be implemented using our ADCs:

• A Basic Guide to RTD Measurements
• A Basic Guide to Thermocouple Measurements

Regards,

Hi Joachim

What I understand from Universal Input is we will able to take different input like RTD-2,3,4 Wire, 4-20mA, Thermocouple, 0-10V these all from one port itself.

Like for 3 wire of RTD, we have to use the circuit given below. So we occupied the 3 Analog pin already. Now if I want to connect thermocouple or 4-20ma circuit as well so we have to use other analog pins or we can connect to these pins only, So how the circuit will be implemented here can you suggest some ideas.. 

Hi Dheeraj,

you would usually use a 4-terminal connector for a universal analog input module, especially when you want to measure 4-wire RTDs as well.
The circuit between the connector and the ADC will then have to be flexible enough, e.g. through the use of switches or Muxes, to accommodate the different input signals through those 4 terminals.

• For the thermocouple you will have to provide means to bias the thermocouple to within the voltage range of the ADC.
• For ratiometric RTD measurements you need to switch the reference resistor and excitation currents in and out of the circuit.
• For 4-20mA loop current measurements you need to switch in a burden resistor to create a voltage that the ADC can measure.
• For 0-10V inputs you need to add some attenuation stage (in case you want to use ADS124S08 or ADS1261), a resistor divider in the simplest case.

You probably also want to add protection for overvoltage and overcurrent.
So as you can see, the circuit can get complicated very quickly.

Regards,

This is ADS125H02EVM Input Pin-out. If i want to connect my 3 Wire RTD here where should I connect?

IDAC1- RTD1 WIRE

IDAC2- RTD2 WIRE

GND -   RTD3 WIRE

4-20mA input is taken from J2.

What about 0-10V input and thermocouple connection? 

can you please check this pin description is correct or not?

Hi Dheeraj,

the connections for a 3-wire RTD could look like the following:

• Lead1 connected to AIN0
• Lead2 connected to AIN1
• Lead3 connected to REFP0
• IDAC1 connected to AIN0
• IDAC2 connected to AIN1
• REFN0 connected to GND
• Place a reference resistor according to the guidelines mentioned in the RTD application note above in place of R14

For 4-20mA inputs you would have to connect a burden resistor between AIN0 and AIN1 (or AIN0 and AINCOM, or AIN1 and AINCOM).
One side of the burden resistor might have to be connected to GND if the common-mode voltage would lie outside the voltage range of the PGA inside the ADS125H02.

A thermocouple would be connected between AIN0 and AIN1 (or AIN0 and AINCOM, or AIN1 and AINCOM). But you would need some means to bias the common-mode of the thermocouple to within the voltage range of the PGA. One of many options would be to connect REFOUT to AIN1 when the internal VREF is enabled.

A 0-10V signal would also be connected between AIN0 and AIN1 (or AIN0 and AINCOM, or AIN1 and AINCOM). Again you need to make sure the common-mode of the 0-10V falls into the voltage range of the PGA inside the ADS125H02.

Regards,

Thanks!

Maybe he's working on a radioisotope thermoelectrical generator (RTG) with a thermopile for harvesting power...