Difference between USB6008 &USB6215 counter input?

[Geert_W]

Hello,

I have to count pulses of a gas meter (5029 pulses = 1 m3 gas).

I did this with a USB-6008 and it works OK. Now I want to switch over to USB-6215 and counting goes wrong.

The USB-6215 counts one cycle random a lot of pulses (e.g. 250) and next cycle 1 as it should be if I select rising edge. This alternating process goes on and on. If I select falling edge then every cycle it counts a lot of pulses more. 

I have the inputs connected parallel so both modules have exact the same pulses. Pulses are 4,7V with low frequency 1 Hz  till max 100 Hz.

USB6008 input in connection = pin 29 (pulse) & pin 32 (gnd)

USB6215 input in connection = pin 1 (pulse) & pin 5 (gnd)

In the MAX same result as with attached LabVIEW program with rising edgge selected.

Who can help me?

Rgds Geert

[ninlmartijn]

Dear Geert,

can you try to enable digital debounce like descibed in this KB. Please let us know if this works,

Best regards,

[Geert_W]

Hello Martijn,

Thanks, yes this works! With digital filtering set on 2,56ms I get with USB6215 same counting as with USB6008.

If I put digital filtering on 6,425 us then sometimes I count too much, at 125 ns this happens regularly but much less then without digital filtering. These are the only allowable settings, on other setting the counter does not work.

Has the USB6008 a standard filter then? With a scope on the pulse input signal I cannot find glitches, so it is for me still a question why a cheap USB6008 performs in this case much more user friendly.

Regards,

Geert Wever
Application Engineer

Honeywell Emmen NL

[ninlmartijn]

Dear Geert,

Thank you for your response. Pplease notice that the USB 6008 has a 5 MHz counter, so it is much slower then the 80 MHz counter from the USB 6215. The values of the digital filter are indeed only  0s, 2.56ms, 6.425us and 125ns.

Best regards,