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Load cell.....fixing to the machine.....

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Full Member level 6
Dec 22, 2006
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Delhi , India
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Dear friends.....

I am using a load cell fixed to a mechanical machine .....which is driven by the motor.........
Now when i connect the oscilloscope probe between the red and black wire of the load cell when the motor is running....there is a huge spike of around 40 - 50V on the wires.....

I would like to know that such a behaviour is undesirable at all since this is going to be connected to the circuit which measures the load cell readings which in actual case is around mV or uV ......

What should be done ..... Iwant to know how a load cell is connected to the body of the machine......
Is this behaviour normal or there is some other technique used so that load cell voltage doesn't vary on motor running connected to machine ....

I want no deviation on load cell reading when the motor runs on the machine......

Plz suggest......
I am posting the signal on load cell red and black wires connected to the machine on which motor is running....

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Use twisted shielded cable between load cell and monitoring system. Add a capacitor 1uF at the sensing terminal. Properly ground the motor. If the motor has carbon brush, make sure that it is not damaged.
Looking at the CRO, the time period of the interference is 30 microsecs ~ 30KHZ, which is where a lot of switched mode PSUs operate. Try switching any PSU off and see if the spikes go IMMEDIATELY, the capacitors will allow the PSU to operate for a second or so. Once the PSU has been located, move it/decouple its output. . to clear the noise. How quickly does your load cell work, a simple low pass filter should be able to clear the noise and give you a useable signal, providing your signal is not above 10KHZ.

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