Noise in load cell

[franz03]

Hi Guys,

How to reduce noise of Load cell?

Do i need to ground or where do i ground the transducer?

We tried isolating the load cell physically and electrically. We tested it far from the motor but when the motor turns on the output signal (4-20 mA) is still affected.

Here is some pictures of the setup:

 

[VEBill]

The pictures don't really provide much useful information.

Are you employing an appropriate load cell amplifier, such as the (for example) HX711 ?

Even if you are, then it's still very common for the readings to contain noise.

 

[Compositepro]

The wires to your load cell act as antennas, picking-up interference. Use shielded cable and twisted wire pairs. The strain gauges on the load cell should also be shielded by covering them with aluminum foil. Are you using the same power supply for the motor and the load cell? That could also be a problem.

 

[BrianE22]

I'd try to find out if the noise was getting in before the input to the conditioner or after the output of the conditioner. 4-20 mA output is generally pretty good for noise so I'd guess the noise was before the input to the conditioner or in the conditioner itself.

Grounding is an art form. Make the change as Compositepro suggested. Try grounding the shield around the excitation pair at the load cell. Then try grounding the signal pair shield at the load cell. Then try putting the ground from the shields at the conditioner. Try one at a time. You don't usually ground at both the transducer and the conditioner.

 

[Comcokid]

The power supply appears to be a small switch-mode type. Just make sure your load cell excitation and whatever A/D measuring the load cell output is powered from linear regulator(s) to reduce the switching noise on your power.

Also, a noise choke, common-mode type, over all lines to the load cell could help. Either a clamp-on type, or 2-3 turns through a toroid type. Since your dealing with motor noise and not RF issues, select a choke core rated for lower frequencies.

 

[zappedagain]

Here's a great book for learning about how to reduce noise. Chapters 9 and 10 will help out in your current situation:

http://www.emiguru.com/books/edn-designers-guide-paypal/

Z