using a FP-AI-100 to read a PWM signal inside a Loop running at 1 second intervals.

[Glendinning Marine]

I'm taking several voltage readings using a FP-AI-100. All but one are steady voltage readings(linear).The one inparticular is a PWM signal running at about 610Hz. All the signals are being read inside a loop taking samples at a 1 second rate. The sampling (testing) last for 4 hours. The problem I have is tring to achieve a steady voltage reading so I can tell if the signal stays between upper and lower limits. The PWM supply is 12Vdc but the voltage range (being sampled) is being varied slowly between 1.85 to 9.35. My sampling is so slow that I'm picking up voltage signals that are outside the set limits and causing alarms. For example when the PWM siganle starts out it's at 1.85Vdc (
if read with a good meter or scope) but connected to the FP-AI-100 and my loop it jumpes from ~.600Vdc to 2.300Vdc. I know why the signal is jumping but I'm tring to find out if there is away to buffer the signal or use some type of an equation to make up for the slow sampling so I can get a steady signal. I know the loop is my problem but I've changed the sampling down to 10msec. (still not fast enough) and it still jumps around. I was just curious if anyone knew a way around this type of problem.

The reason for the 1 sec sampling is to reduce the amount of data being stored. 10msec was just way too much. especially for monitoring purposes.

I guess I need to read the PWM outside of a loop first to see if I can read a steady signal first. Then set the limits out side the lood and run it to a display and into the loop I mentioned above sample it there and store it. I'm not sure so I'll keep tring.

Any help would be appreciated thanks.

[Matthew_Williams]

If I am understanding what you want, it sounds like a low pass filter on the input to the FP module might do it. You'll probably have to make some measurements at different duty cycles to correlate the filter output to specific PWM ratios, but it should be very consistent. Use a 470K resistor and 100uF tantalum cap (values are approximate).


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Matt