Excitation Voltage and Rated Output of Load Cell

[Prarthana_12]

Hi,

I am working on a project for which we are using the load cell of 40Kgs. The data sheets says that-

Rated Output- 1.968/2 mV/V
Allowed Excitation Voltage- 5-18 VDC
Recommended Excitation Voltage- 9-12 VDC
Can some explain me what this means.

Also I am using ADS1232Ref Board which had ADS1232 ADC designed by Texas Instruments. The ADS1232Ref Board user guide says that 'The load cell is excited by +5V Power supply, and ADC's reference is taken from power supply'.

The load cell gives out voltages for the corresponding weight values. The ADS guide says 'The ADS1232Ref can accurately measure any voltage in the i/p range of ADS1232 ADC'. In the data sheet of ADC they have mentioned Supply Range: 2.7V to 5.3V. Is it the supply range needed for ADC or is the range of voltage that ADC can handle and give digital o/p.

I am asking so because the load cell isn't functioning well. Values fluctuate a lot. The ADS1232Ref needs 9V supply.

Thanks

 

[ravindragudi]

The load cell's required input power is not met by the ADS1232 Ref Board's excitation power limits. The load cell wants 9V minimum where as the excitation voltage from ADS... is not more than 5.3V

You need to give minimum of 9V for load cell to function properly.

 

[FvM]

You need to give minimum of 9V for load cell to function properly.

Don't agree. Using 5V excitation shouldn't cause any problems for the load cell. Just connect it according to Ref Board specifications and set the operation for load cell input.

Sensitivity to external noise is of course slightly higher, depending on your setup, a screened cable and loadcell grounding may be necessary.

 

[ravindragudi]

Don't agree. Using 5V excitation shouldn't cause any problems for the load cell. Just connect it according to Ref Board specifications and set the operation for load cell input.

Sensitivity to external noise is of course slightly higher, depending on your setup, a screened cable and loadcell grounding may be necessary.

@FvM, isn't the allowed min excitation voltage (5V) is barely supported by the Ref board? Will this boundary condition doesn't cause issues and reliable readings?

 

[FvM]

Lowering the excitation mainly increases the effect of amplifier noise. It should be expected that ADS1232 is designed to achieve acceptable resolution with 5V excited load cells.

 

[Prarthana_12]

After making the load cell connection. We need to calibrate the board for a particular known weight. But when we put the known weight on the load cell the weight value displayed just goes on increasing. Also the board loses its display suddenly. only each time after resetting the board we get the display back.

 

[KlausST]

Hi,

I agree with FvM, that 5V excitation should be sufficient. But SNR is worse than with 9V.

with 5V and a ratio of 2mV/V at 40kg means that at full range (40kg) the output voltage is 5V x 2mV/V --> about 10mV (with 40kg). Adjust your input amplifier on this.

Maybe you need some analog offset compensation to meet ADC input range.

Also take care to use high quality shielded cables and high quality connectors. Also take care of thermocouple effects causing errors.


***
If you need high quality then use AC excitation and a correlation filter. A lot of effort in HW and SW.

Klaus

 

[ud23]

After making the load cell connection. We need to calibrate the board for a particular known weight. But when we put the known weight on the load cell the weight value displayed just goes on increasing. Also the board loses its display suddenly. only each time after resetting the board we get the display back.

just make sure the load cell shield wire is grounded and proper filtering at your power supply and ADS input channel.