daqmx base voltage error

[Solis]

Thank you John.  When I meant RC cable I meant RCA cable, but yes coaxial cable is the correct term I was looking for.  When I'm back in the lab I'll play around with the wiring again.  I'm pretty sure I tried the shield connected to one of the ground analog inputs, but I will try again.

[Solis]

Sorry, I meant Lynn

[Solis]

Alright, so I've been playing around with the wiring and nothing seems to work for me -_-

I have the coaxial cable for the signal output from the pmt connected to the USB.  The wire is connected to the AI0 channel while the shield is connected to the GND for that channel.  When I run my VI, the data just jumps from 3.88 to 4.02 nonstop, even when I have the power supply to the PMT off.  Any idea what may be wrong?

[johnsold]

Time to break things down.  Disconnect the PMT module from the USB-6009.  Connect the AI0 to GND.  Run the program.  What do you get?  How do you have the inputs configured?  Early in the thread you mentioned changing the configuration.  Please confirm what it actually is now.  Measure the output of the PMT with a voltmeter. What do you get?  Connect a AA battery (or something similar with about 1.5 V output) to the USB-6009 AI0 to + and GND to -.  What do you measure now?  These tests should help you to sort out where the problem is.

Lynn

[Solis]

I'm finally coming back to this project after some time.  I haven't changed the set up much, I have a tick count for my csv file now.  The only thing that bothers me is the ms starts at some random number "207041206" or something similar, is there a way to make it start at 0?

Also I have tried every combination of wiring from my PMT to the USB-6009 I can think of.  I plug the shield into the - and the wire into the + on a voltmeter and read about .001V with no light, then I shine a little light at the PMT and the voltmeter reads about .011V, so it seems to be working with the voltmeter.  The USB DAQ is working because I have tested it with a loop test, connecting AOI and GND to AI0 and ground and it reads a voltage to whatever I set the output to.  I have tried connecting the wires with all combinations, wire to gnd alone, wire to ai0 and shield to gnd, etc.  I cannot figure out what the problem is.

When I run my program, the graph always starts at about 1.35 and just goes up and down between 1.30 and 1.40.  When I switch it to differential mode, it goes up and down between -.1 and 0.

Any other possible suggestions ? Much appreciated.  

My program is attached for reference. 

[johnsold]

Have you tried connecting a different voltage source such as a battery to the USB-6009 inputs to see what you read with that?  This is a way to verify that The AI is working completely independently from the AO and everything else.

What is the output impedance of the PMT module?  Some PMTs look like current sources.

Lynn

[aeastet]

I would also try using DaqMX (Measurement and Automation Explorer) to read the voltage for the channel. This will tell you if it is a connection problem or software problem.

[Solis]

Thanks again for all your help guys, here's where I'm at now.

The PMT did indeed have a current output so I recently ordered and received a preamplifier that converts current to voltage.  (The manual is attached)

Now I think I've ran into some more wiring issues.  The amp manual says there is a +5V and -5V connection along with a GND connection.  I want the amp to be powered by the AO of the USB-6009, but it only has slots for AO0 and AO1.  I've tried connecting the +5V from the amp to the AO0 and the -5V to the AO1 and set each output to those values and connected the GND wire to the GND connection for AO0.  I've tried to get a reading from the amp which is connected to the PMT but I don't seem to get any reading with my program or with a voltmeter.  I seem to have tried all sorts of combinations, leaving the -5V out, or putting the -5V wire to GND, but nothing seems to work.  Any suggestions? I have also attached my updated program for reference.

Your continuous help is more than I could have asked for, I really appreciate it, and I am determined to finalize this program.

[johnsold]

Did you look at the specs of either the amplifier or the USB-6009?  The amplifier's current requirement is 30 mA.  The USB-6009 AO limit is 0 to +5 V and 5 mA.  You cannot power that amplifier from the USB-6009.  No matter how you connect things, it will not work.  You will need a separate power supply for the amplifier.

You also do not need a 50 MHZ amplifier for use with the ~20 kHz USB-6009.  Did you try a resistor? Put a 10000 ohm resistor across the current output of the PMT and set the USB-6009 to its most sensitive range.  At 100 uA output this will produce 1 V.  The PMT data sheet you posted does not specify a compliance voltage for the current output, so you may need to reduce the resistance and accept a smaller voltage.

Do you have anyone around who understands electronics who could help you?

Lynn