ADC input 0..20mA 0..10V protection circuit - Page 1
Forum section: electronics / projects

author: lk.dgironi
author_rank: Regular Contributor
timestamp: May 16, 2024, 09:56:25 am
content: Hello,I'm building a dual purpose 0..20mA 0..10V to 0..5V circuit to connect sources to ADC.It also features protection.I've simulated it and it seems to work correctly.I'm not sure about filters cap, they should go up to 10k without problems.R6 will be 51k + 2k2 in real implementation, and R2 will be 500.Also the opamp MCP6001 or dual or quad version depending on how many input I need.It is designed to be attached to a ADS1115, so I think I'll go for MCP6004.Simulated diode are BAS40, I think I'll go for BAS70.Attached the LTSpiece simulation source and and a simulation image.Do you have any suggestion?

author: S. Petrukhin
author_rank: Super Contributor
timestamp: May 16, 2024, 11:41:46 am
content: I will join the question and add a little bit: please advise specialized input chips 4..20, 0..10?

author: lk.dgironi
author_rank: Regular Contributor
timestamp: May 16, 2024, 11:49:29 am
content: Do you mean changing the post title?Indeed one of the suggestion was about the op amp to be selected.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: May 16, 2024, 11:55:47 am
content: Quote from: lk.dgironi on May 16, 2024, 11:49:29 amNo, no. The topic is the same, maybe someone knows a ready-made solution. Those answering your question may know the CHIP that is ready for use.

author: lk.dgironi
author_rank: Regular Contributor
timestamp: May 16, 2024, 12:00:46 pm
content: Ok! Now I get it

author: lk.dgironi
author_rank: Regular Contributor
timestamp: August 06, 2024, 07:57:38 am
content: Just to let you know.Find attached the schematic with actual values.

author: selcuk
author_rank: Frequent Contributor
timestamp: August 06, 2024, 09:18:08 am
content: I used MAX197 in the past for inputs and AD5751 for outputs. But they are not affordable for many projects.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: August 06, 2024, 10:23:49 am
content: Quote from: lk.dgironi on August 06, 2024, 07:57:38 amI think there is mistake converting current to voltage...

author: S. Petrukhin
author_rank: Super Contributor
timestamp: August 06, 2024, 10:28:20 am
content: I'm trying to use this scheme (from datasheet of HCNR200-500E):

author: lk.dgironi
author_rank: Regular Contributor
timestamp: August 06, 2024, 10:31:24 am
content: Thanks all.@S. PetrukhinBy simulation (and by a test circuit I've built), current is detected when (I'm referring to simulation file) the INc is connected to INn, and both to the -currentSource, then INp to the +currentSource. So in the schematic should be detected when AnalogIn- is shorted with the current sense resistor.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: August 06, 2024, 10:38:02 am
content: Quote from: lk.dgironi on August 06, 2024, 10:31:24 amI'm sorry, didn't immediately understand that current mode is switched on by jumper.

author: lk.dgironi
author_rank: Regular Contributor
timestamp: August 06, 2024, 11:57:06 am
content: That's fine.One think I've noticed is that if i use a current generator like the one in the picture in current passive 2/4 wire mode (figure 3. first diagram). I've to set a gain of almost 1.004 to transform 20mA to 5V on ADC. If I connect the same generator (or a sensor) in current passive 3/4 wire mode (figure 4. first diagram) I've to set the gain x4, so almost 4.016 to transform 20mA to 5V on ADC. I don't get why but it's like so.

author: lk.dgironi
author_rank: Regular Contributor
timestamp: August 20, 2024, 12:51:53 pm
content: Edit: my mistake, I was reading the output from ADC transformation in code.So the gain it's still x1 to transform 20mA to 5V for both generator mode.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 20, 2024, 04:25:03 pm
content: TPS2661 a buck well spent.