Trying to use SCXI-1128 independent mode for 64x1. Demo doesn't correct issues

[Andyoxf13]

I'm trying to use the SCXI-1128 with the independent topology as both a 32x2 and a 64x1 switcher. I have no problems using it as a 32x2, but when I try to control the HLSELECT and 1WIRE relays, I get errors. I can see them as "open", but if I try to "close" either of them I get an error or a no path exists message. I've tried to use the demo from a previous post:
"How Do I Program the SCXI-1127/1128 in Independent Mode as a 64x1 Multiplexer?"
but it still doesn't allow me to utilize the 64x1 configuration. Am I missing something here? Why won't LabView allow me to connect HLSELECT and 1WIRE and how can I get around this problem? Has anyone had success with using the 1128 as a 64x1 m
ux. Just to fill in the rest of the hardware blanks, my communicating device is a 4060DMM and can only be used as a traditional device. I also have a SCXI-1331 attached to the front end of the 1128. Physically, I have a 1k resister from ch0+ to 1_wire_lo_ref and that's what I'm trying to measure with the DMM. As I said before, I have successfully measured voltage and resistance in 32x2 wire mode. Any help would be appreciated!
Thanks,
Andy

[Guy Ferraro]

Andy,

The NIDZ doc:
http://sine.ni.com/apps/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3E95956A4E034080020E74861&p_node=DZ52331&p_submitted=N&p_rank=&p_answer=&p_source=External
explains how to connect any 64 channels to COM0+ (OUT0+) while connecting 1wirelowref to COM- (OUT0-) when you use the SCXI-1127/1128 in independent mode and with niSwitch Control a single Switch.vi

If you are just trying to use the 1128 as a 32x1 or 64x1 Mux you do not need to use it in independent mode with niswitch Control a single Switch.vi nor to worry about HLSELECT and 1WIRE relay.
You can simply:
1) Set your wire mode in MAX in the module property by clicking in the channel tab and selecting All channels (end of the list) and 1 wire.
2) Use niSwitch Connect Channels.
vi with names like ch0 (ch0 to 63 allowed) and com0 to route ch0+ to out0+ and 1wirelowref to com0-. You don't even have to actuate HLSELECT or 1WIRE explicitly.

If you must use INDEP and niSwitch Control a Single Switch.vi then make sure all your channels are set in 1wire mode in MAX.
In the Demo1127_1wire_Connect.vi, you do not need to actuate HLSELCT or 1WIRE. This is done automatically you when you select 0-31 or 32-63.
To connect ch0+ you will need to select ch0 and 0-31.
To connect ch0- you will need to select ch0 and 32-63.

If you connect 1K between ch0+ and 1wirelowref you will probably measure 1.4K or 1.5K due to the path resistance of the SCXI-1128.

[Andyoxf13]

Do you know of a good way to cancel the path resistance?

It sounds like you may have solved my problem here. I'll have to try this out and see. Basically what you're saying is I have to configure all the channels (using MAX) to 1wire. Then I can freely use the independent mode to make 1,2, or 4 wire measurements with full relay control??

If that's the case then you may ignore the following. If that isn't the case, let me describe what I'm trying to do.
I'm glad you pointed out that last piece of information. The reason I want to use this device in independent mode is because I plan to account for the 400 to 800 ohm path resistance of the 1128 (and not have to buy a 4070). I think I can do it, but I'd have to be able to use any channel (ch0 for example) as both a 1 wire and a 2 wire terminal (no need to do it simulataneously, I just have to be able to go back and forth). If I phyically connect ch0+ directly to 1wire_lo_ref and connect ch0- to my 1K resistor and then connect the other side of the 1k to 1wire_lo_ref, I am hoping to be able to determine the path resistance of the entire switch. In order to do this I'd have to take three 2-wire measurements. One from ch0+ to the ref, one from ch0- to the ref, and then I'd have to set up ch0 as a 2 wire terminal and measure the entire path resistance. By using the first two measurments I can calculate the parallel resistance of the ch0+ and ch0- and then I can do some math to cancel out the path resistance. Long story to come to my ultimate question, but I guess what I'm asking is:
Can I use the 1128 in independent mode and configure ch0 as a 1 wire channel (i.e. ch0+ and ch0- with 1wire_lo_ref as a common) and then configure it as a 2wire channel(simply ch0)?
Here's an ascii of the circuit:

|=== 1wire_lo_ref
|
Rpath(1wire)
_____|___________
| |
1K |
| |
Rpath ch0- Rpath ch0+
| |
ch0- ch0+
| |=============com0+
|
|=============================com0-


Thanks for the help, I hope configuring all channels to 1wire will solve my problem.

[Guy Ferraro]

"Basically what you're saying is I have to configure all the channels (using MAX) to 1wire. Then I can freely use the independent mode to make 1,2, or 4 wire measurements with full relay control?"

If you use the switch in independent mode and with relay control, the wire mode in MAX is irrelevant. Since you select which relay you want to actuate, you make the signal route.

If you use connect channels, the wire mode is relevant If you set the wire mode to 1 wire in MAX and use niSwitch Connect you can only use the switch in 1 wire. To use it in 2 wire mode you need to go back in MAX and change the wire mode to 2 wire.

"Do you know of a good way to cancel the path resistance?"
For 1 wire mode, I would set the switch in 1 wire mode in MAX an
d use NiSwitch connect to measure de path resistance of the 64 path by connecting a short between each channel and 1wirelowref.
For 2 wire mode, I would set the switch in 2 wire mode in MAX and use NiSwitch connect to measure de path resistance of the 32 path by connecting a short between each channel + and -.

[Andyoxf13]

Thanks again for all your help. I am still unable to fully control all of the relays in independent mode with relay control VI's. I think I'm going to have to get a NI support package and give them a call...

[Guy Ferraro]

Sorry we couldn't make it work.
Another option would be to be able to use DAQmx descriptor (SC1Mod4) instead of traditional descriptor (SCXI1::4::INDEP) with the use of a NI 4021 (real cheap switch controller).
With the use of DAQmx descriptor the whole problem goes away and you will be able to control every relay on the 1128 as you like.
NI will probably require you to updgrade to the latest NIDAQ 7.2.
Good luck.

[Andyoxf13]

I actually just called them and placed the order. I figure if the 4021 doesn't work, the 4070 will, and if that doesn't work then I may have to find another job!
I truly appreciate the help!!

[Guy Ferraro]

I am sure the 4021 will work for you. NI will not let you quite. Post again if you need help.