9401

[alannspower]

Good Morning:

I have a cDaq 9184 and a ni 9401 module: I am trying to measure two frequency inputs to the ni 9401 with values between 100 to 2 Mhz and the software configuration for each is "large range counter" and "frequency" selected for them on the counter vi inputs. The outputs of both insturments are open collector with 5 volt max and the pull up resistor that can range between 100 and 1000 ohms, the signals are connected to pins 14 (PF0) and 19 (PF3) and both commons are connect as well.

The devices are RADIAN Watthour meters and I can see the acutal values displayed and the Radians and the Radians are compared to a national standard and they have errors between +/- 0.02%, However when I am viewing the values diplayed in LabView the errors are bouncing around +/-10% and it appears to be noise. I have tried everything optical coupling, c mos, schmitt triggers with AND gates and nothing appears to work. So, I verified the resistance between pins 14 and 19 and I am measured appoximately 38 Kohms and then measured both pins to common with a resistance of 8.8 Kohms: shouldn't pins 14 and 19 be infinite?

Thanks

Alan 

[Spicy_Mystery · Accepted solution]

Hi alannspower,

You're right - the resistance should be very high (infinite).  How are you measuring these exactly?  Also, have you tried measuring other pins to see if they have the infinite resistance we would expect?

[alannspower]

Hello:

I am using a multi meter for resistance, voltage, and frequency and radian watt hour meter for watts/VA and the frequency. I removed the module from the daq and took measurements of all the commons just in case pins 1,3,4,6,7,9, 10,12, and 13 are connected together. Now I measured the resistance between pin 1 and all the inputs 14,16,17,19,20,22,23, and 25 with a measurement of 40K, then I flipped the leads with the positive on pin 1 and measured the resistance of the input pins and I measured 9K approixmately on each pin, then from pin 14 to all the other inputs and I measured 40K app.

I have only used it two or three times with a maximum of 5 volts applied and I purchased the product in Sept 2013, could a surge or spike from losing power cause this problem? warranty?

Regards

Alan

[alannspower]

Hello Spicy:

I emailed NI support and William asked a few questions:  

After a bit more reading on the National
Instrument site,  I found a similar problem but the person used a filter
but I knew my signal was clean, so I thought about it and the only thing I did
not change much higher value than the default was the divisor, I used the
calculated value of the frequency that I was measuring and then I had very
stable clean measurement. I would say the counter was hitting the rising slope
of the pulse enough times to cause the error, whew….I am sending you the
picture

Thanks

Alan