ADS1256: 16 channel datalogger

Lidong Yu

Part Number: ADS1256
Other Parts Discussed in Thread: ADS124S08EVM

I want to use ads1256 : two numbers for 10 channel K type thermocouple and 3 nos 4-20 mA input

My question is can I use PGA function individually that is 10 temperature channel for K type with auto cold junction compensation and other three as 4-20 equivalent to pressure range I define in software

Kindly support with application note

over 4 years ago

0 Bryan Lizon86 over 4 years ago

TI__Guru 58781 points

Hi Lidong,

The ADS1256 only has 8x single-ended inputs (or 4x differential), so you would need 2x ADCs to measure >8 channels.

There is also no automatic cold junction compensation with the ADS1256 (or any other device for that matter). You would need a discrete temp sensor or an analog temp sensor such as an RTD or NTC to perform this function.

Here is a link to our thermocouple cookbook document. This has a lot of useful information about how to measure TCs: https://www.ti.com/lit/an/sbaa274/sbaa274.pdf

-Bryan

0 Lidong Yu over 4 years ago in reply to Bryan Lizon86

TI__Intellectual 1756 points

My question is since there are two separate signals one is T/C and other is 4-20 mA so I have to use separate ADC and how to interface with 8 bit micro controller and how to achieve same : rdgs to Micro controller we will discuss later

0 Bryan Lizon86 over 4 years ago in reply to Lidong Yu

TI__Guru 58781 points

Hi Lidong,

You do not necessarily need to use 1x ADC for TC measurements and 1x ADC for 4-20mA measurements. I would take a look at the ADS124S08EVM as an example of how to measure TCs and 4-20mA with just one ADC: https://www.ti.com/lit/ug/sbau272a/sbau272a.pdf

This device EVM has an input path for TCs as well as current shunts: the TCs are shown in section 5.1.1.2 and 5.1.2.3 (which also discusses how to peform cold junction compensation with a thermistor, RT2) , while the current measurements are shown in Section 5.1.3. This will give you a very good indication of how the external circuitry should be implemented. You can then extrapolate that out for 10x TCs and 3x 4-20mA circuits.

-Bryan

0 Lidong Yu over 4 years ago in reply to Bryan Lizon86

TI__Intellectual 1756 points

Thanks
But How to configure T/C , cold junction and 4-20 mA in measurement : It means I have to use PGA and Reference to configure separately and use in software : any application note ???

0 Dale Li over 4 years ago in reply to Lidong Yu

TI__Mastermind 49355 points

Hi Lidong,

Bryan is out until next Tuesday.

Have you checked the EVM user guide in the link Bryan provided above and also the ADS124S08 datasheet? Both documentations provide all information you need.

Best regards,

Dale

+1 Bryan Lizon86 over 4 years ago in reply to Dale Li

TI__Guru 58781 points

Hi Lidong,

I agree with Dale here, I provided a lot of information for you to begin your design.

Can you please make an attempt at putting a block diagram or schematic together and then come back with specific questions?

You can also check out these reference designs for information about how to design systems to measure sensor / process inputs:

-Bryan

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ADS1256: 16 channel datalogger