RTD and electronic signal noise

- S
- sergius
  
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posted
17 years ago

Fri, Nov 3, 2006 11:21 AM

hi there,

I am facing an acute problem with the RTD which I am using for a bioreactor control. A DC motor is used for agitation of the bioreactor. The RTD is a three wired one and it is calibrated everytime before experiment. It gives high and erroneous reading when the agitator motor is switched on. The bioreactor is a bottom driven vessel. I even tried earting the motor and the control panel to minimise the signal noise with little sucess.It has been hindering my experimental work.

Could any of you suggest a solution? Thanks in advance

best, palpandi

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- Paul M
  
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posted
17 years ago

Fri, Nov 3, 2006 1:06 PM

On 3 Nov 2006 03:21:07 -0800, "sergius" proclaimed to the world:

First, if the RTD has a sheath ground, make sure it connects to the case ground on the meter. If there is no sheath ground, then use some braided metal sheathing to put around the lead wires and as much of the RTD as possible, grounding the sheath at the meter case.

If this does not work, separate the metering instrument's ground from the common ground and run a separate earth ground to it. Drive your own ground rod if necessary.

But I suspect that this DC drive setup for the stirrer has some problems that is producing lots of noise that should not be there. Figure that problem out and the metering problems will likely go away.

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- Jerry Avins
  
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posted
17 years ago

Fri, Nov 3, 2006 5:26 PM

I will give odds that the motor current flows through some part of the measuring circuit. Grounding is needed to eliminate capacitive coupling, but too much grounding creates ground loops. Look for them and break the loop.

Jerry