What could cause and how do I clear an Analog to Digital (ADC) error?

What could cause an A/D conversion error?  How do I clear an Analog to Digital Converter (AD or ADC) error on my Hardy controller?

If the load cell is not connected, wired incorrectly, mounted upside down or damaged, you could have a voltage out of the expected range, 0 to +15mV, causing the ADC error.

On a Hardy Process Solutions unit, the usual cause of an A/D error is that the signal output from the load cell is out of range. Check the DC mV reading between +Signal and -Signal. This should be from 0 to +15 millivolts DC. Any negative value less than -0.3 or any value above 15.3 millivolts will trigger the A/D conversion error.

NOTE:  The HI 3300, HI 3030, and HI 6000 series units have a calibration sensor type setting for higher and negative mv/v rated load cells.  If the unit is set for one of these other settings, the range of the input would change accordingly, but the cause, symptoms and troubleshooting would remain the same. 

Another cause of an A/D error would be incorrect sense voltage, as the sense voltage is the reference voltage for the A/D converter. If the sense voltage is disconnected or incorrect, the A/D converter can drift out of range. You can check the voltage between +sense and -sense. This should be equal or slightly less than the excitation voltage minus the voltage dropped over length of cable and/or barriers if used. If your module has jumpers installed between the excitation and sense, then sense volts should be EXACTLY the same as excitation volts.

If your sense lines do not have jumpers installed, verify the sense wires are terminated correctly in the summing junction box. The sense voltage should be slightly lower than excitation voltage. This would depend on the length of cable.
Longer cable = higher resistance and lower sense voltage.

If barriers are used then the sense voltage will be about 2 volts lower than the excitation voltage at the unit. Jumpers must be removed and sense wires installed when a barrier is installed.

You will need to check the excitation, sense, signal wiring and installation to verify there is no problem. With an Excitation wire and signal wire swapped the signal voltage will read 2.5vdc. If the sense lines or jumpers are not properly installed there will be an imbalance in the reference voltage and be out of range.

On the newer model load cells it is very difficult to install the load cells upside down, but it is possible. Other reasons for an Analog to Digital error condition are if the overload bolts are too tight or if the shipping brackets are left on the load cells.

The HI 2110 WI and HI 2151/30WC can also display a HI or LOW indication that is the same as an ADC error.
The HI 6000 series units will show '------' across the display if the input is out of range.

If wiring and installation are good, then you may have a damaged load cell or controller input circuit. Try swapping load cells, removing the load, and swapping instruments to help determine the location of the error.

The other possibility is the A/D converter section of your Hardy controller has failed. If all the voltages check good and you still have an A/D error, and cycling power does not correct the problem then your Hardy Instrument should be returned to the factory for evaluation/repair.

You can request a Return Authorization

Please review additional Web Tech answers for information on how to troubleshoot your load cell and controller.  Pay attention to the articles on lockup and static protection.