Best way to measure current and transmit to Computer

Thread Starter

Lancelot97

Joined Aug 20, 2017
5
Hello everybody,
I'm doing some testing on our circuits, and I automated most of the process with a bed of nails created on a 3D printed model. I'm communicating with a PC via COM (Serial) Port. What is really missing to automate everything are some current and voltage measurements. We're doing the voltage measurements with an oscilloscope and the current measurements with two multimeters. These Fluke multimeters unfortunately cannot communicate with anyone.
So, what I'm asking is: what is the best way to do this kind of testing? By buying new multimeters with an optical/wi-fi/any kind of connection with the PC or by building a custom circuit with current and voltage monitor with an appropriate IC, and developing all the software to communicate with the PC?
Please take in account that I'm measuring 10uA-50mA with one tester and up to 0.6A with the other one. I have past experience with ICs with so much tolerance, that they made the whole measurement useless.

I'm new to this forum, if I'm doing something wrong, or in the wrong place, just tell me!
 

danadak

Joined Mar 10, 2018
3,793

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ebp

Joined Feb 8, 2018
2,332
You need to have a clear idea of the precision and accuracy you require. You must also consider where in the circuit currents are to be measured. Measuring with one side of a meter connected to circuit common is a far different thing from measuring current where both meter leads are volts or tens of volts away from circuit common. The latter may require precision differential amplifiers or even fully isolated circuitry. That applies to every channel to be measured. Depending on what you require it can be less expensive to use multiple floating ADCs and galvanically isolate the digital data. Isolated DC-DC converters are cheap, but noise can be a serious problem.

If you decide to build something, be exceedingly careful if an analog multiplexer is involved, either as part of an ADC or as a separate IC. Some will not tolerate signals even a few tens of millivolts beyond their supply rails. One overdriven channel can scramble all channels.

Many multimeters in the thousand dollar bracket have Ethernet and/or USB intefaces that are galvanically isolated.
 

danadak

Joined Mar 10, 2018
3,793
In edp's post mention is mode of high side sensing vs low side, and impact
on CM range allowed by A/D. This is current sensing by inserting a low value
R in + power supply to load vs in ground side of load and measuring V across
that R to calc current.

In PSOC, if you use DelSig, bypass its input buffer, its inputs will CM outside
supply rails by 100 mV. Thats generally enough to do current sensing. For example
1 ohm in high side will give you 100 mA max, .1 ohm will give you 1A max, etc...

And at 20 bit resolution will yield required range/res of current measurement you
want. The onchip +/- .1% reference will set your absolute accuracy (along with
rest of error budget, eg. R accuracy, A/D error...).

Regards, Dana.
 

Thread Starter

Lancelot97

Joined Aug 20, 2017
5
Thanks everybody!
I am a sort of "factotum", I'm an embedded programmer, Electronic designer and I also enjoy programming desktop programs.
So far, the best solution I have found is to read multimeters (U1252 from Keysight) with a PC, using C#. Since I'm already connected to other Serial ports to get the board status and progress with testing. I have chosen this way also because I can run without the program simply by disconnecting the multimeters from the PC and reading them manually.

Again, thank you so much and Best Regards to everybody!
 

MrAl

Joined Jun 17, 2014
6,979
Hello there,

When i want to transmit to the PC computer i usually use RS232. That's because the protocol is simple enough and you can bit bang a microcontroller to do RS232 or use a built in peripheral RS232.

If you buy a meter that has RS232 you can easily read the port with your custom desktop computer using the Win API (assuming you are working on the Windows platform of course).
Keep in mind though that most meters only do one channel, so if you need two channels (current and voltage) you either have to buy another meter or figure out how to multiplex the readings from a single meter where you switch between current and voltage. The latter is hard to do though so i'd go with two meters unless of course you want to buy ready made devices that can handle the task.

The meter protocols are so simple if you have ever done any hardware programming you will find it a relatively simple task even if you start from scratch and follow the RS232 protocol standard by reading about it online.

If you only have USB ports and you want to do RS232, then you can get RS232 to USB adapters that will give you an RS232 port from a USB connector, and they are cheap these days.
 
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