ADS124S06: ADS124S06

Hi Bosco N,

Are all thermocouples differential measurements such that you need two analog inputs per thermocouple?

You said the sensor has "inbuilt CJC" - is that an additional sensor that needs to be measured by the ADC? If so, what is that sensor's output voltage?

If you need >6 analog inputs then you could also use the ADS124S08, which is just the 12-channel version of the ADS124S06. Both of these ADCs are intended for measuring thermocouples and other analog temperature sensors.

Bosco N said:

also datasheet mentions Programmable Data Rates: 2.5 SPS to 4 kSPS . (is this per channel or it will be divided into 6 channels)?

Yes, the sample rate is effectively divided by the number of channels you need to measure. Refer to the second column in tables 13 (low latency filter) and 15 (sinc3 filter) in the datasheet for the conversion time per channel in a multiplexed system.

You can also reference this app note for more information about measuring thermocouples with ADCs: https://www.ti.com/lit/an/sbaa274a/sbaa274a.pdf?ts=1759503691895&ref_url=https%253A%252F%252Fwww.google.com%252F

And this app note for information about conversion latency in multiplexed delta-sigma ADCs: https://www.ti.com/lit/an/sbaa535a/sbaa535a.pdf?ts=1759503992126&ref_url=https%253A%252F%252Fwww.google.com%252F

-Bryan

Hi Bosco N,

You can measure 6x differential inputs using the ADS124S08 then

The thermocouple measurement accuracy is directly related to the CJC measurement accuracy. So if your the CJC measurement is 1% accurate for example, so are the thermocouple measurements. Therefore, you generally want a high accuracy sensor to measure the CJC. The ADS124S08 internal temperature sensor is not the best candidate for this task. Most customers end up using a thermistor, then measuring the thermistor with the ADC as well. This is shown in the thermocouple application note that I linked to in my last post. There is also an example CJC circuit on the ADS124S08EVM

-Bryan

Hi Bosco N,

Bosco N said:

Is there a isolation for the for the TC which we can try? pl., suggest.

Can you explain what you mean by isolation? Are you talking about digital isolation between the ADC and the MCU? Or are you expecting common-mode differences between the thermocouples? If so, how much? Or maybe you mean something else? Please explain

Bosco N said:

Also, we have another application which is required to measure 4-20ma loop current from pressure sensor. can we use the below schematic?

Yes you can see that the ADS124S08 can measure a 4-20mA loop using the provided schematic. Just make sure that the voltage across the shunt is never larger than the ADC can support (generally limited to 5V, refer to the datasheet for more information) 

-Bryan

Hi Bosco N

Are you expecting a common-mode voltage of 250V between different thermocouples? For example, if one thermocouple is at VCM = 0V then another thermocouple could have VCM = 250V? If so, then you will need isolation between each thermocouple channel, which is 6 isolators per board. This requires optoisolators or some other form of analog isolation. You can check out our ISOMxxx portofolio of opto-emulators for options, or use a MOSFET

Or are you expecting that all thermocouples will have the same VCM relative to each other, and the VCM = 250V is between the controller ground and the thermocouple voltage? if so, then digital isolation should resolve this issue. You can operate the ADC with only 4x digital lines if desired: SCLK, DIN, DOUT/DRDY, and CS. Use something like ISO7741 for this purpose

-Bryan

Hi Bosco N,

Bosco N said:

But what about the DRDY,START/SYNC,RESET. Lines, without these pins can we use the device?

Please review the datasheet, most of these questions are already answered in that document.

Bosco N said:

J-type EMF is –8.095 to 69.553mv. PGA to be selected is 32(FSR) is that right?

Your max signal is 69.553mV * 32 = 2.226V. So as long as your reference voltage is larger than this value you should be able to measure the signal. Of course you also nee to make sure you meet the ADC input range and PGA common-mode range requirements as specified in the datasheet

Bosco N said:

Hope the device can be configured for few channels as Diff and Single Ended.?

Yes, the device can support differential and single-ended signals. The ADC always measures between the channels you select for AINP and AINN, it does not care what those signals are as long as they are within the input range of the ADC and meet the PGA common-mode range requirements as specified in the datasheet

-Bryan

Hi Bosco N,

Please review this application note for more information regarding your most recent question: https://www.ti.com/lit/an/sbaa535a/sbaa535a.pdf?ts=1760274558388&ref_url=https%253A%252F%252Fwww.google.com%252F

-Bryan

Hi Bosco N

I have used TMUX1109 (4-ch differential mux) in the past for temperature measurement circuits. This comes in a 2.6x1.8mm QFN package to keep the overall solution small

The TMUX1309 is a lower cost, lower-specified version of the TMUX1109. The TMUX1309 is not pin compatible to the TMUX1109 however

-Bryan

Hi Bosco N

Thanks, please start a new thread in that case since that new post will have nothing to do with the ADS124S06 or this topic

-Bryan

Hi Bosco N,

You can click on my name (Bryan Lizon86) and click "send a private message". This will allow you to share your information with me outside the public e2e forum

-Bryan