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strange problem

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Hi, I've a pressure sensor , which is connected to a uC , and we used it for a tension machine which measures the strength of metals like ferrite , the sensor have a strange voltage its 40V AC , i measured it from earth to it , i dont know from where this residual voltage on it , and when i discharge this charge, it works good , i dont know from where this builds up .. what could be the problem ??
 
Hi, I've a pressure sensor , which is connected to a uC , and we used it for a tension machine which measures the strength of metals like ferrite , the sensor have a strange voltage its 40V AC , i measured it from earth to it , i dont know from where this residual voltage on it , and when i discharge this charge, it works good , i dont know from where this builds up .. what could be the problem ??

Please provide more details , your details are too less to analyse.

Can you provide the schematic / wiring details of your sensor . Including its powersupply requirement , earthing ?. How do you filter the sensor inputs and and outputs?

Where did you made the measurement ? 40V from earth to sensor where?

What is your Grounding and isolation schemes.
 
Ok, im sorry for not providing more details, btw , I'm a new engineer in this company , that's why i dont know more details.

The schematic is so simple , its just a Gnd , 10V , output connected to the pressure sensor, its power supply comming from a power supply box , the sensor output isnt filtered , its connected to the uC directly .
There is no isolation scheme , that machine were working in the past , i dont why its not working now .

The 40V AC measured from the ground of the machine to the sensor's input .
 
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Is the sensor ground connected to the machine ground?
 
But is the sensor GND connected to the case (machine ground)?
 
If the 40VAC is from the ground of the machine to the sensor then why is that a problem if the sensor ground is not connected to the machne ground?

And how do you discharge an AC signal?
 
You can't really discharge an AC voltage, it's either there or it isn't.

What does the AC voltage measure after you "discharge" it?

How long does it take before the sensor stops working after this?
 
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Perhaps you could permanently connect some relatively high value of resistor that would keep the circuit discharged without affecting the sensor output (say 100k ohms).
 
Sorry , the 40VAC is from the GND of the sensor to its input.

I dishcharged it like discharging a capacitor using a resistor .

One simple answer could be your sensor has subcum to noise and is faulty, did you check this sensor with other part? . Placed a CRO at its output and see what is happening? . You must place an RC or LC filter at sensor output to catter this.
 
One simple answer could be your sensor has subcum to noise

I'm not usually a grammar nazi, but - "succumb".


Ahmed, please get a number or a picture of that sensor. It's probably some sort of load cell.

What makes you think this piece of test equipment "works good" after you discharge this thing? Do you have calibrated references to compare tension readings against? If it's a malfunctioning strain sensor, I'm not sure I would trust those readings.
 
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