Help With Agilent 34908A

[ap1150]

Hi I am using labview 7.1 with an Agilent 34970A that has a 34908A 40 channel MUX module.
I have no problem using labview to control the channels, I can open and close then easily. My only trouble is reading and writing from the channels. I am trying to send a signal to a channel that is closed, and when I run the VI the the Agilent beeps with an error.
can anyone help?
thanks
AP1150

[Dennis_Knutson]

have you run the error query VI to determine what the instrument error is? What VI are you running when you get the error? The example VIs like Single Point Read and Scanner Demo close relays themselves or set up a scan list for opening and closing.

[ap1150]

That brings up another problem. I was unsure how to write to the open channel. I just created a simple VI with a Visa write function in it. I did not run the Error Query VI yet and When I do will will post what the error is.
Thanks for your help

[Dennis_Knutson]

I don't know exactly what you mean by writing to the open channel. What is the command you sent with the VISA Write?

[ap1150]

The Error I get is: -103, "Invalid Separator"
The 34908A module is a 40 channel MUX, where all the channels are left open. If you want to talk to a specific channel, you close it. Sorry for the confusion. Once I have the specific channel ready I used a VISA write function to send a signal to that channel. I used a input string of 010.

[Dennis_Knutson]

That's not the way the way the box works. Once you close a channel, then you want to measure whatever signal is at that channel. That would be a command to the internal DMM. The actual command you send would depend on what you're trying to measure - voltage, frequency, temperature, or whatever. It would be some form of a MEAS command. The string "010" is not a valid command. You cannot "put" anything on a channel with any command. Channels are for sensing. If you want to output something from the 34970, then you would need something like the 34907 module which has both digital and analog output.

[ap1150]

I forgot to mention that I do have a 34907A multifunctional module. Do I need to use that in order to send data to a channel, or can channels only be read?
thanks for your replies, they have been very helpful

[Dennis_Knutson]

If you have a 34907, then you can physically wire from one of it's ouputs to one of the 34908 input channels. All that would do is read back the 34907 outputs. You cannot wire one of the 34907 outputs to the common point of the 34908 mux so if you wanted to mux a digital or analog output to 1 of 40 points, the box doesn't support that, at least not without modifying the 34908 by removing some relays and adding your own wiring. With the 34904 4x8 matrix switch, you have some flexibility but you would need an additional 34970 mainframe for 40 channels.

[Dennis_Knutson]

I want to take back some of what I just said. I took a look at the 34908 schematics and I think there's a way to mux an external signal. H com and L com of the mux is available. I never paid any attention to this because most of what we use is the 34902 and it has 100 ohm resistors in series. The 34908 doesn't have these so you could wire an output of the 34907 to the 34908 com connections and mux outputs. You might have to send a specific command to open the backplane switch so that the internal DMM (if present) is not connected. Normally the backplane switch is closed automatically.

[ap1150]

Ok, I have connected the common high on the 34908A to bit 0 on port 2 of the 34907A. This seems to work. When I put a 1 in bit 0, and close channel 201, I read a high. When I put a 0 in bit 0 it reads a low. The only problem with this is that the whole signal is high. What if I wanted to send the channel a 1010?
AP