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Electronic scales sensor

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klug

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tenzo sensor

Hi!

I am making revers engineering of electronic scales. I need to make my own circuit using sensor of this scales. I see that sensor is some metallic bar (14x15x150mm), and it has ceramic plate in a center of a side. There are 6 wires comming to that plate. I have measured voltage on them, but as I see there are no changing of voltage when load is applied.

1 - GND
2 - 1.309 V
3 - 1.309 V
4 - 1.309 V
5 - 2.618 V
6 - 1.309 V

As I see with oscilloscope there are only direct current coming to sensor from a circuit.

What is principle of this sensor? - as I think it is some piezo element.

How to make measuring of a weight with this sensor?

Is there some circuit diagram of scales with this type of sensor?

Thanks in advance! klug.
 

jourval

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how to build electronic scale

I not thing that it is piezo
Piezo gives signal proportional to dF/dT that is very
difficuilt for use when your measurement is statical.
Check 2 options: it can be hall elements and scale plate is magnetic
or it can be brige of tenzosensors that give disbalance voltage,
when tham get small deformation (not direct pressure! try to deformate a bit plate with sensor)
 

klug

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sensor scales

Thanks Jourval!

I have not disassembled all mechanic construction and do not see this plate directly, but as I see through narrow slot, there are 4 or 5 black strips on ceramic plate with some traces routing to them, 2 located at an angle of 90 degrees to metallic bar, and 2 at 45 degrees to it (90 between them), and one is parallel to bar. You are right - it is some bridge circuit - maybe tensosensors.

Is there any information about tensosensors and circuit diagrams based on them?
 

jzaghal

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tensosensor

Hi,

I think this is a Load Cell that you have.
Search for the word TEDEA using google.

Good Luck. 8O 8O
 

jourval

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tenzo-sensor

In this case, I am sure, that it is tensosensors.
Standard way to measure deformation and/or displacement
with tensosensors are wittston bridges. Every bridge must contain
2 sensors that get deformation in the same direction (I mean 2 for axis 0 degree for first bridge and 2 for 45 degree axis), you need 2 sensors for temperature compensation. Tensosensor is semiconductor device
that change it's resistivity with deformation. It is linear for small deformations (1-3% resistivity change). You need connect diagonal of bridge to +/- inputs of operational amplifier with low drift and offset.
Resistively of most tens sensors is a few kilo ohm, so better to use OA
with bipolar input. BTW you measure V and V/2 voltages, so you surely have bridge on your device!
I think you"ll need some summing device for get sum signal for 2 pairs of
sensors (0 and 45 degree) in this case weight measurement will be independent from mass placement (more or less).
Try "to google" "weight processor" - it will help.
If you want, I can send you Orcad schematic with main connection principles
 

klug

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electronic weight scale schematic

Thanks, Jzaghal!

I do not know how this sensor is named exactly, load sell, tenzosensor, tensosensor or strain gauges.

I lost my patience and have disassembled that construction. I have found bridge circuit with 8 resistors. They are located in this way:




and all circuit diagram is here:



As I understand, some of this branches are for some compensation :
temperature and so on. Maybe it is wide using sensor and there is complete circuit for it? What is principle of exact measuring here?
 

klug

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how to mak an electronics scales

Thanks, Jourval!

Yes, I have measured them, they have about 10 kiloOhms.
This circuit becomes more complicated than I realised.

As I understand R2 and R7 are in the same orientation, so they are making reference voltage (without dependency of temperature).

R1 and R8 are located on the same way, so they are making reference point for second bridge.

So, measuring branche in the first bridge is R3/R4 , and in the second R5/R6.

I do not know, what diagonal pair R3/R4 is making here? Is it for some torsion measuring?
 

jourval

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sensors used in electronic scales

you must apply reference voltage to point 5
and you'll get two bridges. Voltages between points 3 and 6
and 2 and 4 will be proportional to load - it's all.
Connect these points to differential amplifiers, and then send them to
any adder and ADC or 2 ADC and make "+" on your processor.

Don't forgot low pass - your signal is slow!
 

luben111

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amplifier tenzo resistor signal

Hi,

As I know Analog Device have some special for scales ADC converters. They are 24 bit resoltion, and use Vref from part of volt.

In your case you see tenzo sensors with temperature compensation. The change of voltages and currents is extremely small - you can't get them with multimeter.

They have excellent temperature compensation, because they use bridges and the scheme of Vref somehow is connected with the temperature (Vref goes to the resistors of the aluminium block).

My advice is to search into ANalog Device for ADC converters/scale/24 bit resolution

Regards
Luben
 

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