Delay of one physical channel

[MogaRaghu]

I have a machine code running for the past  one year . ( PCI 6229 +  LV7.1 + Win 2000 )

Four differential ananlog channels configured for 0-10V .

Since one week I have a problem :

Ch_0 and Ch_2 are for a pump rpm and pump flow.  (As the rpm increases the flow also increases and the plot is used to validate the pump.)

For no apparent reason,  recently the  flow readings are lagging behind the rpm values. And the faster the pump rpm is accelareted the more the lag.  Nothing wrong with the pump when tested on another machine.

The data are acquired one sample once every 50ms in a timed loop.  The rpm data is from an optical encoder converted to analog value and the flow readings are from a flow meter, once again by pulses to analog conversion.

I am planning to feed a common sweep signal to both channels and plot them. But in the meanwhile, till that is possible, is there any way  that one channel in a PCI card can lag like this due to a malfunction ?

Thanks

Raghunathan

[Albert.Geven]

Hi

I can think of only one possibility. The inputs of your IO card are very high impedance, and when a low impedance value from your pump is connected a few electrons stay behind when the next channel is read.

First check if you are measuring differential or single ended. (you can see that in MAX)

second I would wire channel 1 (not used now) to zero volt or reference.

third I would measure channel 0,1 and 2 always together and that each 100 ms (or 50)

The time between the channels is so as short as possible.

And check if your phenomenem is still there.

succes