question about load cells and the AD8222 amplifier

Thread Starter

Gibson486

Joined Jul 20, 2012
336
First question is about load cells. If they give me a 1m/V spec, that means that it will span 5mV with 5V excitation WITH RESPECT to ground? However, the whole span, with respect to the negative side would double (ie 10mV)?

Second, I have the AD8222 amplifier in house. I see in the spec sheet it says that the max voltage swing is (−VS + 1.1) to (+VS − 1.2). Does this mean that with a 5V supply, I cannot get a swing of more than 2.4V?

Bringing it all together, it would not be possible to take this load cell and use it with this amplifier to get .5 to 4.5V out with just a 5V supply?
 

Reloadron

Joined Jan 15, 2015
6,058
If the load cell sensitivity is specified as 1 mV/V then with 5 volts excitation applied at full scale load the load cell output will be 5.0 mV with respect to the load cell common of Vout. Just as an example and only an example most load cells are a 4 wire device, there is + and - Excitation and a + and - output from a bridge. Vout is the output. In the case of a Tension and Compression cell the output will range from a positive to negative Vout. Do you have a data sheet for your specific load cell?

As to an operational amplifier?
Second, I have the AD8222 amplifier in house. I see in the spec sheet it says that the max voltage swing is (−VS + 1.1) to (+VS − 1.2). Does this mean that with a 5V supply, I cannot get a swing of more than 2.4V?
Yes, if you want a full swing you need a rail to rail op-amp. If you use a +5 and -5 supply Vout will not exceed -3.9 to 3.8 volts.

Ron
 

Thread Starter

Gibson486

Joined Jul 20, 2012
336
Load cell is an lbs200 from Flutek. I think this is a tension and compression. When I measure from + to - and put a full load, I get a 10mV
differential from a 5V supply and it is a 1mV/V scale. I am trying to do everything from a single 5V supply, so split rail op amps are a no no for me.

edit, looks like the AD8822 was a bad selection. I will try the INA326 or something else similar. Thanks!
 
Last edited:

Reloadron

Joined Jan 15, 2015
6,058
Yes, if you want to amplify a load cell (strain gauge) output an instrumentation amplifier is a good choice.

"The INA326 and INA327 (with shutdown) are high-performance, low-cost, precision instrumentation amplifiers with rail-to-rail input and output. They are true single-supply instrumentation amplifiers with very low DC errors and input common-mode ranges that extends beyond the positive and negative rails. These features make them suitable for applications ranging from general-purpose to high-accuracy".

That should work out fine as it is a rail to rail instrumentation amplifier which is what you want.

Ron
 
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