Principle
and Overhaul of DT electronic
scale
DT
electronic scale consists of sensor, amplification circuit, A/D
transformation circuit, display circuit, chip microprocessor, memory and
power source etc. Sensor transforms weight into voltage signal
correspondingly, then to be amplified, thereafter enter into A/D
transformation circuit, turn into digit, and at last digital weight is
displayed on the indicator screen after calculated by chip microprocessor.
Ⅰ
Operating
Principle
1.
Sensor
DT
electronic scale users aluminum alloy double-hole beam-style resistance
strain sensor. In terms of different weight and precision, select proper
sensor.
2.
Amplification Circuit
Positive
and negative terminal of signal output of sensor respectively link
positive and negative input terminal of the integrated operational
amplifying circuit. And this magnification times is decided by R1. When
no-load, voltage of output terminal (foot 6) should be lower than half
power source voltage, exactly to say from 6.5V to 7.3V. If above 7.5V, A/D
transformation will fail, meanwhile scale will display “F----5”.
There should be more than 1.5V voltage difference between full-load
voltage and no-load voltage of foot 6, and no-load voltage is higher than
full-load voltage; if less than 1.5V, calibration will fail. Bigger
resistance value of R1 is, bigger voltage difference is. IC2 is a filter
putting out equal voltage to IC1. According to these values, we can judge
whether sensor, IC1 and IC2 work normally or not.
IC3
is a sampling voltage tracking generator. For example, when R6, R5, R4
respectively are 4K, 3K, 1K, voltage on foot 6 of IC3 is 9.3V; if R6, R5,
R4 are respectively equal to 2K, 1K, 1K, voltage on foot 6 of IC3 will be
11.5V.
3.
Principle of AD Transformation Circuit
AD
circuit adopts double-integral theory. At first, it integrate signal
positively (notice: voltage into which weighing signal is transformed
after amplified must be lower than midpoint voltage of power source in AD
part; then will have a favorable integration). And then, integrate it
negatively using constant voltage higher than midpoint voltage. Time clock
calculates the time which negative integral needs when back to original
state; this timing value is inside code namely.
On
the whole, if these parameters above changed, the part of AD will not work
well: Displaying “F----5” means that there is some trouble in
artificial circuit. First check whether sensor broke down or not. Detect
whether voltage on foot 6 is normal or not; if abnormal, sensor might
break down.
Ⅱ
Operation
Turn on the scale
first. Then it display “------”; following is from “F----2” to
“F----9”.
If
stop when “F----3”is shown on, this means there is some key conducted.
If
stop when “F----5” is shown on, this means A cannot be transformed
into D.
Usually,
voltage into which weighing signal is transformed after amplified isn’t
lower than midpoint voltage of power source (in AD part). Generally
because sensor is not good or improperly linked, or maybe occur some
problems with amplification circuit.
After
self-detection, it displays “1”; one chirp of buzzer is heard
simultaneously; then display “0”. If displaying “F----L”, this
means base weight is too light, or very small value is transformed in AD
transformation, all these may make result wrong. Common reason is
zero-shifting of sensor.
And
“F----H” means overload, that is to say outside upper limit of range
ability. Press calibration button, it will display “C-----” normally
after a while. Though “C----F” indicates zero point isn’t stable. It
is necessary to reset, correct again.
Caution:
before correction, pare first as usual.
When
display “C----F”, there may be another problem that base weight of
tray is too heavy. Sensor needs to repair.
If
5-6 minutes passed by after correction, there is nothing displayed; this
represents value of AD transformation cannot get to minimum limited value
(may relay when calibration time is unstable; calibration value must be
gained when stable, otherwise wait until stable).
There
is a minimum limited value which must be reached; then can enter into
counting state, or else cannot (notice: when counting, unit weight cannot
be too light, especially cannot be less than 1g, or else occurs unstable
end of digit counted.
Ⅲ
Trouble-shooting
symptom
|
cause
|
1.display
“F----5”
|
1.do
not add tray
|
2.sensor
doesn’t
work well
|
3.without
15V power source
|
2.display
“F----H”
|
1.overload
|
2.sensor
doesn’t
work well
|
3.data
display not stable
|
1.sensor
contacted conducting wire, and so on
|
2.15V
power source not stable
|
3.
units on circuit card welded virtually
|
4.crystal
oscillator broke down
|
5.
capacitor is leaking electricity
|
6.sensor
went bad
|
7.bad
reception of sensor
|
8.4066
broke down
|
4.display
“F----3”
|
1.some
key has been conducted or under short circuit condition
|
5.display
lacking of segments
|
1.bad
core of chip microprocessor
|
2.some
bad segment of numeric code tube
|
3.74∠S273
went wrong
|
6.display
lacking of figures
|
1.bad
core of chip microprocessor
|
2.triode
invalid accordingly
|
3.numeric
code tube invalid
|
7.signal
alarm alarming continually
|
1.bad
core of chip microprocessor
|
2.crystal
oscillator broke down
|
3.reset
capacitor invalid
|
8.display
“8”
wholly or not display
|
1.chip
microprocessor invalid
|
2.crystal
oscillator broke down
|
9.linear
weight display incorrectly
|
1.improper
amplifying resistance
|
2.improper
adjusting linear resistance
|
|