Input Design for Datalogger

Hello,M.Pathma,
If you may give us more detail information, we can give you more supports. Now I give you some simple advice. First, use a differential AMP, then RC filter, and condition the signal to ADC spec. The below circuit is FYI.

  If you have some problem, pls contact me.

  AWan@premierelectronics.com.cn

Best regards

Alex Wan AWan@perier

Hi, Alex,

Thanks for your feedback,

What I am looking for is and input section which will have the capability to measure the voltage, current and temperature Assume the design will have IN+ and IN-, the customer can connect either thermocouple, voltage or current source to this input.

Setting the configuration correctly the system will measure temperature, voltage or current. The reading ranges I have indicated in my 1st posting.

This design will be used in Industrial Environment, thus all the protection and precautions should be followed.

Hope the above is clear, if not please define what type of information you need.

M.Pathma

Hi, Alex,

Thanks, I will work in your direction, of-couse my requirment is that no-jumper usage, I will replace with Mosfet or CMOS switchs.

I need to study which OP-AMP will be more stuiable for my appliciaton.

As for the current, I think wanted to have the shunt resistor ourside the system, but need get approval from requestor.

Thanks again.

If you have some referance design for system like this OR system with partial (such as temperature only or current only), will be great.

Regards

M.Pathma

Hi, M.Pathma,
It's my pleasure.
Yes，using OP may be more suitable for your appliciaton than optical-coupler，thus circuit is more simple.

Best regards
Alex Wan

Hi, Alex,

I will definitely need to isolate the sensor and main processor, because this is an industrial design.

There is no requirement to have isolation between channels, so, i'm considering the following configuration.

There is few major problem,

• we need to have about 8-12 opto-isolator.

• the ADC is 24bit, but I doubt we can achieve this resolution, I am committing on 12-bit only (due to multiplexing effect)

• The setting for all the channel must be the same, meaning, if channel 1 is configure to 50V, then all the channel should be the same, I do not know if this is agreeable

• Sampling rate is depend on the switching speed of multiplex IC and ADC stabilities , I doubt I can produce anything faster the 10 sample per sec per channel, when I need to read all channels

Feedback on the above is welcome or better approached is appreciated.

Regards

M.Pathma

Promosys Technology

Hi, M.Pathma,

If you think there is too many opto-coupler，you can select 8ch ADC, for example TI ADS1243IPWTADS1243IPWT, so that the number of opto-coupler can be reduced.

As for the 24bit ADC, I think it does not matter with 24bit or 12bit, because I guess you are selecting AD7712 for the purpose of using the internal PGA.
The problems mentioned above are not critical, I think the key problem is the third one. You can try to use seperated ADC and PGA, and place opto-coupler behind pre-amp, thus the funciton of PGA and ADC can be both achieved with flexibility.

FYI ony.

Best regards
Alex Wan

Hi, M.Pathma,

If you think there is too many opto-coupler，you can select 8ch ADC, for example TI ADS1243IPWTADS1243IPWT, so that the number of opto-coupler can be reduced.

As for the 24bit ADC, I think it does not matter with 24bit or 12bit, because I guess you are selecting AD7712 for the purpose of using the internal PGA.
The problems mentioned above are not critical, I think the key problem is the third one. You can try to use seperated ADC and PGA, and place opto-coupler behind pre-amp, thus the funciton of PGA and ADC can be both achieved with flexibility.

FYI ony.

Best regards
Alex Wan

Hi, ALex,

Thanks for your feedback, you are right, I just got the email from the stakeholder of this project that item 3 is not agreeable. According to them, each channel should be configurable.

I will consider your proposal.

thanks for your asstiance.

M.Pathma