@Adam Equipment Company 2004
6
7.0 GAIN AND ZERO ADJUSTMENT
The circuit board assembly has an amplifier that must be adjusted if load cells are
changed. The amount of adjustment and the details of what is adjusted will depend
upon the values observed from the A/D converter.
The basic adjustments are for gain and zero. The gain is adjusted by observing the
A/D counts at no load and when a mass equal to the full capacity of the scale is
placed on the pan.
The A/D counts at no load and the increase in the number of counts when a full
capacity load is added are as follows. The no load readings are all done with the
pan in place on the load cell.
Model #
AQT-200
AQT-
250
AQT-600
AQT-
1500
AQT-
2000
AQT-
5000
Maximum
Capacity
200g
250g
600g
1500g
2000g
5000g
No Load range
of A/D Counts
5000 -
15000
2000 -
8000
2000 -
8000
5000 -
15000
2000 -
8000
2000 -
8000
Increase in
counts when
maximum load
is added
80,000 -
100,000
20,000 –
35,000
35,000 –
50,000
80,000 -
100,000
20,000 –
35,000
35,000 –
50,000
Gain Resistor
normally used
R49
250 ohm 300 ohm 250 ohm 390 ohm 390 ohm 195 ohm
If the A/D counts for the no load condition (Zero) are too low, increase the value of
R47 or R46 (which ever is in use) to typically 1700 ohm. If the A/D counts at zero
load are too high, it will be necessary to lower the value of R47/R46. Both the
resistor locations marked R46 and R47 are in parallel.
If it is required to change the gain of the amplifier to make the increase in the
number of counts when a maximum load is weighed, then R49 should be changed.
A larger value for R49 corresponds to a lower gain.
The resistors used for R49 and R47 should have very low temperature coefficients.
Less than 50ppm/ºC is recommended.
The changes for gain will affect the zero readings and should be done before the
changes to the zero readings.
