Adam Equipment AQT Series User manual

@Adam Equipment Company 2004
Adam Equipment
AQT SERIES
SERVICE MANUAL
ADAM EQUIPMENT CO. LTD.,
P.N. 6200, Rev A, September 2004

@Adam Equipment Company 2004
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CONTENTS
1.0 AQT FEATURES .................................................................................. 2
2.0 AQT SPECIFICATIONS ....................................................................... 2
3.0 INTRODUCTION .................................................................................. 3
4.0 REMOVING THE COVER .................................................................... 4
5.0 LOAD CELL DAMAGE ......................................................................... 4
6.0 PRINCIPLE OF OPERATION............................................................... 5
7.0 GAIN AND ZERO ADJUSTMENT ........................................................ 6
8.0 ERROR MESSAGES............................................................................ 7
9.0 TROUBLE SHOOTING GUIDE ........................................................... 7
10.0 AUTO CALIBRATION........................................................................... 8
10.1 AUTO CALIBRATION (FOR AQT 200 ONLY) .................................. 8
10.2 AUTO CALIBRATION FOR ALL OTHER MODELS.......................... 9

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1.0 AQT FEATURES
•Auto shut off
•Auto zero tracking
•Auto backlight (optional)
•Low battery indication
•g/ct/oz/dwt conversion
•Large LCD (6 digits 15 mm high)
•Large square SS pan
•Net weight/stability indication
•Auto calibration
2.0 AQT SPECIFICATIONS
Model # AQT-
200
AQT-
250
AQT-
600
AQT-
1500
AQT-
2000
AQT-
5000
Maximum
Capacity 200g 250g 600g 1500g 2000g 5000g
Readability 0.01g 0.1g 0.1g 0.1g 1g 1g
Minimum
Capacity 0.2g 2g 2g 2g 20g 20g
Resolution 1:20,000 1:2500 1:6000 1:15,000 1:2000 1:5000
Repeatability
(Std Dev) 0.02g 0.1g 0.1g 0.2g 1g 1g
Linearity ± 0.02g 0.1g 0.1g 0.2g 1g 1g
Units of
Measure g / ct. / oz. / dwt/ tL.H
/ tL.S /tL. t g / ct. / oz. / dwt kg / g / lb / oz
Stabilisation
Time 3 seconds 2 seconds 3 seconds 2 seconds
Operating
Temperature 0ºC to 40ºC 32ºF to 104ºF
Power
Supply 9-12 VAC @ 100ma adapter or 6x AA batteries
Calibration Push button calibration using external mass
Calibration
Mass 200g 250g 600g 1500g 2000g 5000g
Display 6 digit LCD, 15mm digits, with backlight
Draught
shield 145 x 145 x 120mm 5.7" x 5.7" x 4.7" N/A.
Balance
Housing ABS Plastic
Pan Size 100mm
diam.
3.9" diam.
120 x 120mm
4.7" x 4.7" 145 x 145mm 5.7" x 5.7"
Overall
Dimensions
(w x d x h)
145 x 210 x 40mm
5.7" x 8.3" x 1.6"
without breeze shield
Net Weight 1.2 kg, 2.6 lb
Features Low battery, Stable and Zero indications

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3.0 INTRODUCTION
The scales are all based on resistance strain gauge load cells. The load cells
output a small voltage in response to a load placed on the weighing platform.
The voltage is in the range of approximately 10mv for a full capacity load.
The signal from the load cell is amplified by an instrument amplifier with
differential inputs. This voltage is then sent to another amplifier that will filter
the response to eliminate high frequency signals (above 5 Hz.). This voltage
is then presented to an A/D converter for conversion to a digital value for use
by the microprocessor.
It may be necessary to replace a load cell if it is damaged. In this case it may
be necessary to change resistors on the PCB to force the A/D counts to be
correct. A table showing the resistor values and A/D counts follows.
The scales have the ability to view the counts from the A/D converter. Press
the [Units] key then turn on the scale using the [On/Off] key. Release the
[Units] key to show the A/D counts.
The load cell connections are:
Before any changes are made to the scale, it will be necessary to trouble-
shoot the problems and determine the best method to solve the problems.
Refer to the Trouble-shooting Guide for suggestions.
PCB main board
Red (E+)
Black (E-)
White (S-)
Green (S+)
J3

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4.0 REMOVING THE COVER
If it becomes required to remove the cover, you should be very careful as
pulling or pressing on the load cell during this procedure can damage it very
easily, especially on the lower capacity balances.
When removing the screws (1 screw for the plastic pan support and 4 small
screws below the scale) hold the cover to the base and ensure not to press on
the balance case as the load cells can be damaged.
On some units the load cell is attached to the cover, on larger capacity units
the load cell is attached to the base.
The load cells are protected by overload and under-load stops. These stops
are either plates that contact the cover or screws that are accessible from the
outside of the scales.
Refer to the Trouble-shooting Guide for the possible causes of any problem.
5.0 LOAD CELL DAMAGE
If a problem is suspected with the load cell or A/D converter press the [Units]
key and then turn the scale ON to observe the A/D counts. The counts should
go from a smaller value (typically 2000-8000) to a larger value as weight is
added to the pan. The value shown should also be stable.
If the A/D counts are outside this range or cannot be seen then it will be
necessary to trouble shoot the load cell, load cell connections to verify the
load cell is working correctly and has not been damaged.
The most common reason for a scale to fail is that the load cell has been
damaged. The damage can be due to two primary causes. The first is the
physical damage due to an overload or an impact from the side and the
second is damage due to the environment, such as moisture, extreme heat or
a cut cable if the cables are exposed.
With the AQT scale it is possible the load cell is damaged such that the scale
still operates when the scale is calibrated but not when a small mass is put on
the pan. This will become apparent when the scale reads correctly at the
calibration mass but is not correct at lower masses. The scale may still zero
OK after power is applied but it will not register a weight value for smaller
weights.
Check the A/D counts in this case.

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6.0 PRINCIPLE OF OPERATION
The strain gauge load cell is a method of measuring the amount of stress put
onto a metal structure due to a weight being supported by the structure. The
stress is measured using 4 strain gauge sensors mounted in a particular way
on the metal structure.
These 4 strain gauges are connected in such a way that they form a
Wheatstone Bridge. See the figure below. In the simplest load cells there are
only the 4 resistances of the strain gauges to consider. Normally without a
load on the load cell, all the resistances are the same. However, when the
load cell has a weight on it, two of the strain gauges will be in compression (A
and D) and the resistance will decrease and the other two will be in tension (B
and C) and their resistance will increase.
350 ohm
350 ohm
350ohm
350ohm
AB
CD
+E
-S
-E
+S
BALANCED BRIDGE
10 VOLT POWER
SUPPLY
Vout = O VOLTS,
BETWEEN +S AND -s
351 ohm
349 ohm
351ohm
349ohm
AB
CD
+E
-S
-E
+S
UNBALANCED BRIDGE
FULL CAPACITY LOAD
ON THE LOAD CELL
10 VOLT POWER
SUPPLY
Vout = 0.028 VOLTS (28mv),
BETWEEN +S AND -s
This will cause the bridge to become unbalanced. When the bridge has a
voltage across it from +E to -E then the signal output at +S and -S will show a
voltage of zero volts with no load and a small voltage proportional to the load
as the load is increased. Typical load cells show 10mv of signal if the
excitation voltage is 5volts and the load cell is fully loaded.
To check the load cell, apply power to the scale and measure a voltage
between the S+ and S- wires when de-soldered from the PCB. The voltage
should be less than 2millivolts with no load on the scale, increasing as the
load is applied. The voltage between the E+ and E- wires should be 5V.

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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.

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8.0 ERROR MESSAGES
When power is first applied to the scale a check is made to assure the A/D
counts are within a normal range. If an error is shown at this time the A/D
counts are either too high or too low.
EEEEE A/D counts at turn on are too high.
ADLOW A/D counts at turn on are below zero.
In either case, check the A/D counts as described above. Verify the load cell,
load cell wiring and the A/D counts are acceptable. Try to calibrate the scale
if the A/D counts are acceptable.
During normal operation, the display may show an error under these
conditions:
EEEEHI Overload
EEEELO A/D value too low
Low battery, replace battery if used. Check the
external power supply if batteries are not used.
9.0 TROUBLE SHOOTING GUIDE
PROBLEM POSSIBLE CAUSES
Display is blank Mains power is turned off
No turn on test Power supply not plugged in
Power supply faulty
Display is disconnected or faulty
After turn on test Pan not installed
Error message is Unstable weight
Displayed Load cell damaged
Display is unstable Drafts or air currents
Obstruction under pan
Sample is moving (animal weighing)
Vibrations through table
Temperature changed dramatically
Power supply faulty
Weight value incorrect Calibration error, Recalibrate
Unit calibrated with inaccurate weight
Balance not level
Obstruction between sample and cover or
breeze shield
Wrong unit of weight displayed

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Cannot use Full Capacity Over load Stops hitting pan support
or hitting bottom of load cell
Shipping screw not removed from base
Electronic problem on A/D
Load Cell Damaged
Not Linear Overload stops hitting too soon
Load cell damaged
A/D damaged
Capacitor(s) on A/D PCB damaged
Off Center Loading error Overload Stops not correct
Load Cell damaged
Keyboard failure Keys damaged
Cable to display/keyboard not connected
Incomplete LCD display Poor contacts on LCD
Damaged LCD or circuit board
Backlight does not turn on Backlight module damaged
Backlight power supply failed
10.0 AUTO CALIBRATION
•Calibration may be required when the balance is initially installed
or if the balance is moved from a location.
•With time and use, mechanical deviations may occur. Therefore
calibrate the balance whenever the best accuracy is required or
when any deviation is observed during weighing a test weight.
•Before calibrating it is necessary to have the proper calibration
weights. The weights should be OIML Class M1 type or better.
If you do not have proper weights do not attempt calibration.
Model # AQT-200 AQT- 250 AQT-600 AQT-1500 AQT-2000 AQT-5000
Calibration
Weight 200g 250g 600g 1500g 2000g 5000g
10.1 AUTO CALIBRATION (FOR AQT 200 ONLY)
•Before entering calibration mode, press [On/Off] to turn the
power on for 1 minute.
Enter calibration mode
•Press [On/Off] to turn the power off.
•Press [Unit] first and then press [On/Off], while keeping the
[Unit] key pressed. The display will show the A/D value.

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Calibration
•Wait for the stable indicator to be displayed,
•Press [Unit] - the display will show "  ", with the "  " flashing.
Place the 200g weight on the platform. A beep will be heard
after a few seconds and the display will show "  ".
•Press [On/Off], to turn off the power. Press [On/Off] to turn on
the power again.
•Place maximum weight (200g) on the platform to verify weighing
is correct. If not, repeat the calibration.
10.2 AUTO CALIBRATION FOR ALL OTHER MODELS
•Before entering calibration mode, press [On/Off] to turn the
power on for 1 minute.
Enter calibration mode
•Press [On/Off] to turn the power off.
•Press [Unit] first and then press [On/Off], while keeping the
[Unit] key pressed. The display will show the A/D value.
Calibration
•Wait for the stable indicator to be displayed,
•Press [Unit] -the display will show "  ". After 2 seconds,
the display will return to A/D value.
•Place the maximum weight (eg.2000g for AQT2000) on the
platform.
•After the stable indicator is displayed press [Unit]
•The display will show "  ". The calibration in complete now.
•Press [On/Off] to turn the power off. Press [On/Off] to turn on
the power again,
•Place full weight (eg.2000g for AQT2000) on the platform to
verify weighing is correct. If not, repeat the calibration procedure.