Timers Read-Errors with U3 when closing-opening coils | LabJack

Timers Read-Errors with U3 when closing-opening coils

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benjiworld's picture
Timers Read-Errors with U3 when closing-opening coils

Hi everybody. We have a serious trouble working with our U3-LV. We are measuring the speed of a rotating shaft connected to FIO4 by using timers configured @ 4MHz via python and LJFuse. Another shaft is measured with a counter activated to anoter FIO port. Everything works great, until the moment we manually close a brake coil located a few meters away from the magnetic speed sensors used on shafts. When closing/opening the coil, we receive strange and unexpected values of timers. We are not able to understand if the values obtained are really the gap between the past two rising edges, as it should be, or if it's just an error produced by U3. We tried to use two different opto-isolated power sources to separate the power of sensor with respect the power of coil. The result is the same error. We need some help to understand what could be the cause and the solution to the problem. We guess there could be two possible scenarios: 1. sensors are very sensitive to the magnetic induction generated by the coil opening/close, so inducted currents are flowing inside cables with resulting errors on measurement; 2. U3's logic/ground levels are sensitive to inductive currents fluctuation with resulting errors on measurement; Any kind of help will really appreciated. Thank you. Benjamin.

LabJack Support
labjack support's picture
The first guess is that the

The first guess is that the coil is putting noise on to your signal wires and creating lots of extra edges.  Try testing with a Hardware Counter rather than a Timer.    Or connect your signal to both a counter and the timer a the same time.  Watch the counts you get under normal operation, and then see what you get for counts when you operate the coil.

If you do indeed see something happen to the counts, we can then tackle that and it is easy to see when you get back to proper count levels.