Sensor value periodically spikes and then settles

[aguy004@aucklanduni.ac.nz]

Hi there,

The issue is, I have two sensors (for measuring torque and acceleration) connected to a PXI-6221 and both the outputs of the sensors spike periodically (every 5 seconds or so) and then settle back down. Any help on how to remedy this would be appreciated.

Regards

Alim

[Henrik_Volkers]

Some more information about the setup (kind of sensors (output impedance?) , type of measurement, type of cables&length), would be helpful.

First thing is usually to find the source of the spike. Is it mechanic or  EMC or ??

One way would be to mechanically decouple the sensors (but keep the electrical connections the same) and have a look at the signal.

Can you hook up a (analog?) scope instead of the 6221?? Since the 6221 have a 10GOhm input impedance, and the scope usually a 1MOhm you might see differences.

But if you still see the spikes it eases the hunting of the source.

[aguy004@aucklanduni.ac.nz]

Hey thanks for the suggestions,

I used a multimeter to measure the voltage output of the sensors and the spikes weren't seen, which makes me believe its the 6221 and because both sensor outputs are spiking at the same time when plugged in.

Is there a way to confirm my suspicions?

[johnsold]

Alim,

The multimeter is probably way too slow to see the transient effects. A scope is much more informative.

Did you try Henrik's suggestion to decouple the sensors from the mechanism?

Most likely the problem is either a real mechanical effect that you were not expecting or some electrical interference.  The probablility that it is in the 6221 or the sensors is quite small.

Lynn

[aguy004@aucklanduni.ac.nz]

Hey,

I was going to decouple the sensor, but then realised the spikes are only seen when the servo motor is running... So i'm guessing its running some interference. Is this likely to be the case? The respective wiring are well seperated if that is any help.

Regards,

Alim

[johnsold]

Alim,

Certainly correlation makes the motor and its driver highly suspect.

Please describe your apparatus in more detail.  What is the purppose of the servo motor? How is it coupled to the sensors? Is the servo drive analog or digital? Can you tell what the servo is doing at the instant that you see the spikes?  Are the grounds or signal reference points of the sensors and servo drive connected?

Lynn