ni 6008 acquiring digital inputs from an absolute encoder.

[fedelo]

Hi, i'm a student working on my master thesis.

I'm trying to acquire 9 digital channels from a 9bit absolute encoder on the NI-USB 6008 but i'm encountering the following problem.

I'm powering the encoder trough the 0V (GND) and +5V ports on the NI-USB 6008, and if i read the digital outputs directly from the pins

of the encoder with a tester, without connecting them to the NI-USB 6008, i see +5V or 0V with respect to GND.

If then i wire the outputs of the encoder to the NI-USB 6008 digital ports, the readings of the tester,  are 5V or 3.6V with respect to GND, so basically

when i try to acquire the signals with Labview, they never switch to logic low.

I'm a doing something wrong or is it a problem with the NI-USB 6008?

Thank you for the help.

[alex83]

Hi,

It seems that NI-USB 6008 works well and that the encoder is not able to force low the digital output signal.

I think that this problem could have different explanations:

- the encoder needs a pull down resistor in order to work properly

- the encoder try to force low the digital port while the 6008 is forcing high the same port

- the encoder is damaged

Try to take a look at the encoder manual in order to see if the encoder needs some additional circuitry to work properly.

Alex