Hello everyone,

So im trying to interface a load cell like this one with a lab amplifier

Usually thoose are used with this proprietary board (HX711) but i can't use it here because of the very low sample rate of theese circuit (80SPS)
I want to use this cell in a PID regulation loop so this is much too low, i need to use the cell coupled to an amp board and an arduino (i will be using a arduino DUE which ADC sample rate is 100 kS per second)

But have some trouble interfacing it with the lab amp im using :


All wiring schematic i've seen for this application seem to use a amplifier configuration where there is 2 input separate from ground (here V+IN and V-IN, not sure how this called)



But my amp is not like that, the input is only one pin, the other "input" pin is the ground, same as output, continuity test show connection between input and ouput ground

I tryed this wiring, but output show no response to load cell force, all i read is noise from the power supply




Im lost here, maybe my lab amp is not suitable for this work, is that case i will make a custom one, but if it is possible to avoid it that would be nice !
Thanks a lot !

 

What you need is a differential amplifier.

Google instrumentation amplifier and you will find many circuit diagrams showing three op-amps configured to create the differential amplifier suitable for your application.

 

hi,
Look at Fig #41 of this AD623 datasheet for an example of a Differential OPA. [IA]
If you build your own IA, then use 0.1% resistors and rail to rail OPA's.

E

 

You want as mentioned a good IA (Instrumentation Amplifier) The AD 623 is a good choice as is the AD 620. You can as mentioned roll your own amplifier or a simple Google of "load cell amplifier circuit" will bring up a few dozen hits as can be seen in the link. Some with data out and some with simple scaled analog outputs of current or voltage out. In addition to using good precision resistors in rolling your own your excitation voltage needs to be extremely stable, as in a precision reference.

Ron

 

Hello,

You could have a look at the INA125.
https://www.rs-online.com/designspark/using-the-ina125p-instrumentation-amplifier-with-a-load-cell
That chip has its own reference for powering the loadcell.

Bertus

 

Thanks a lot for all this informations,
I think i will go for the INA125 first because it look very easy to wire, then i will consider the AD623
I found this pre-made AD623 board, do you think it is good ?
https://www.ebay.fr/itm/AD623-Progr...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649

Also, can you tell me more about the amp rack a have ? I understand that this not a differential amplifier, but how would you call it ?
Many thanks

 

hi lou,
That AD623 module requires SPI control of the Digital Gain potentiometer, do you have a MCU on the project that could provide the SPI control.?

The Rack appears to be a single ended general purpose OPA.

E