Not really a direct NI related question

[m-s]

 But I do not know a better place to pose this question (suggestions are welcome).

I have a set of instruments that all need to connect to the same probe station at different points in time during the course of a measurement.

They have coax/triax outputs. Is there a GPIB controlled BNC multiplexer on the market that I could use with LabVIEW. Googling has led to a few candidates but none of them appear to be LabVIEW compatible (they have their own software, which is useless for my application since I need LabVIEW to be able to control what switches when) ?

[nitad54448]

hi

do these instruments have GPIB or other type of interface ? if so, you could easily control them with LV. For connection, maybe a swicth with a matrix card or multiplexers can do the trick. I am using the 7001 from keithley and 36790a (or something like that) from agilent.

NI has many multiplexers and matrix cards (I didn't used them, yet)..  bottom line is all these can be controlled with gpib, serial, usb, etc

N

[F._Schubert]

Apart from the options already mentioned (NI and Keithley), I also did such switching 'circuits' on my own.

Start with the instrument (instrument's manufacturer) if there is a suitable extension for an existing instrument. Some only allow multi DUTs on the same instrument, which won't help you. Also many only come in certain form factors, for my Apps NI only provided solutions using PXI or SCXI. Having those platforms not present would require an expensive chassis.

Apart from the avialable form factors, current and voltage ratings are of concern.

Doing it on your own isn't to difficult. Either use a standard electrical installation system (e.g. Wago on DIN rail). Most instruments including NI cards come with some digitial signals (5V) that you can use for control. You might need optocouplers if switching higher voltages. Second option is to do your own PCB using relais or transistors (depending on electronic specs) with driver circuits (UNC-family). This gives you max flexibility. I like NIs CA-1000 box as the PCB housing as it has connectors to their cards (and in your case BNC connectors).

Also consider the channel count. 100s of BNC connectors need space!

Felix

[RTSLVU]

The Agilent 34970A DAQ/Switch has RF multiplexer modules in both 50 and 75 ohm.

The RF multiplexers are arranged as two independent 1 x 4 multiplexers, each with a common shield and a switched center conductor. Connections can be made directly to SMB inputs with 2 GHz usable bandwidth, or to the BNC-to-SMB adapters provided with 1 GHz bandwidth. Multiple banks may be cascaded together for applications requiring even larger topologies-- create a stubless 16:1 multiplexer in a single frame.

http://www.home.agilent.com/agilent/product.jspx?cc=US&lc=eng&nid=-33640.536881544&pageMode=OP

I haven't used any of the RF modules but the Agilent 34970A DAQ/Switch is our engineering workhorse around here.

Unless you have to ue GPIB I would recomend the 34972A as it has USB and Ethernet (LXI) interface in place of GPIB.

[Sean_F]

Hi m-s,

A couple questions for you. How many channels are we talking about? What bandwidth do you need? How quickly do you need to switch between devices? If you only have a couple channels you probably won't want to invest in a PXI or SCXI chassis. What you could do is use LabVIEW to control cheap Digital I/O module (USB 6501) to drive a relay. This module doesn't support hardware-timed I/O so if you need deterministic switching you might be more interested in an X-Series multifunction DAQ. Let me know a little bit more about your application specs and I'll try and make some more specific recommendations.

Regards,

[m-s]

Hello Sean,

Thanks for your response.

To answer someone else's question - no, these do not have a IEEE-488 instruction set (at least the manufacturer does not advertise it). Just a windows program that will help you control it. Useless.

To answer your question,

1. I need 4-6 channels.

2. Bandwidth does not have to be terribly high - just a few 100 Hz will do, I think.

3. Over a period of about 10-50 ms, if possible. Slower may be acceptable.

A DAQ sounds like an overkill for this.

[Sean_F]

Hey m-s,

Yeah, if you're only using 4-6 channels then you probably don't want to invest in a PXI/SCXI chassis. I think the cheapest option for you would be to buy some inexpensive switches and control them with an inexpensive DAQ. The price of the DAQ will depend on if you need hardware-timed control. If the 10-50 ms spec is the switching period then I would suggest hardware-timed I/O. The 6320 would be a good option. 

Best,

Sean

[m-s]

Thanks, but I can't use the 6320. The target application is running on a Linux machine. I will keep looking, but thanks for the idea.

[RTSLVU]

You haven't mentioned a budget ,and that is really going to be the defining factor.

I did a little searching at my usual test equipment suppliers and found that the vast majority of commercial RF switches designed for automated testing are made for high bandwidth applications and start in the 15K$ range.

The aforementioned Agilent 34970A with one RF MUX module will run about 2K$

Since your bandwidth requirements is relatively low, you could ham it up with something like these Remote RF Antenna Switches intended for ham radios. But you would also have to design you own switch control. You could start with a USB-DIO1024 from Measurement Computing I prefer their USB DAQ's and DIO's over NI's and they say they have some Linux support, but it look's like it's third party drivers so your mileage may vary...