Does NI not have any switches capable of Hardware Handshaking using the PXI lines (aka Setup 3)?

[RVallieu]

https://www.ni.com/docs/en-US/bundle/ni-switch/page/switch/scanning_single_mod.html

Shows the following Set-up types:

Determining the Scanning Setup

The scanning setup is dependent on your hardware and triggering scheme. Based on your hardware and triggering scheme requirements, choose one of the following scanning setups:

PXI/PXI Express Scanning—Synchronous

• Setup 1—Using Internal PXI Trigger Lines
• Setup 2—Using AUX Trigger Cable Connected to Front of PXI/PXI Express Switch

PXI/PXI Express Scanning—Handshaking

• Setup 3—Using Internal PXI Trigger Lines
• Setup 4—Using AUX Trigger Cable Connected to Front of PXI/PXI Express Switch

The following page must be incomplete as it doesn't indicate that ANY NI-Switch is capable of Set-up 3 from above(?):

https://www.ni.com/docs/en-US/bundle/ni-switch/page/switch/scanningg.html

I need a 2-wire switching mode Hardware Scanning Capable NI-Switch to work with a PXI-4071 for measuring Thermistors...

Is it true that none of the switches from NI Support Setup 3?

[TobiasG · Accepted solution]

This information is much harder to find online than it should be. It looks like the topic on this is available but hard to find and the formatting is messed up. We have filed a couple internal Bugs (2498290 and 2498289) to make it easier to answer this question in the future. The information is available on the individual Devices pages, but those are currently only available in the offline help after installing NI-SWITCH.

That said, to answer your question here...

All PXI/PXIe NI-SWITCH modules support handshaking (hardware) scanning with the following exceptions:

• SwitchBlock
• PXIe-2524, PXIe-2525, PXIe-2526, PXIe-2737, PXIe-2738, PXIe-2739, PXIe-2746, PXIe-2747, and PXIe-2748

NI generally recommends using software-timed handshaking with our NI-SWITCH and NI-DMM instruments for the following reasons:

• It allows reconfiguring the NI-DMM during execution.
• Autorange on the NI-DMM can often be avoided with software-timed scanning, but is required with hardware-timed scanning. The increased time for autorange more than cancels out the performance benefits of hardware-timed scanning.
• The newer PXIe-4080/1/2 NI-DMMs are much faster and the software-timed performance will be at a similar level as handshaking with older NI-DMMs.

[RVallieu]

That was the page I referenced as not showing any S3 Setup availability.

Interesting that NI recommends software timed.  I want my system to be able to scan while my code checks for a command and then comes back to handle reading the number of samples from the DMM buffer.

[RVallieu]

Am I correct in my understanding looking at the example code that when scanning with NI-Switch and NI-DMM that it is expected that all the Thermistors are the same type and coefficients?  I don't see a way to load an array of coefficients.

[kirsch]

I think that’s what Tobias alluded to with “It allows reconfiguring the NI-DMM during execution”.

In order to do hardware scanning / handshaking between a DMM and a switch, you use multi-point mode in NI-DMM. One limitation of multi-point mode in NI-DMM is that all the measurements must use the same exact configuration. The auto-range comment is an extension of that: if all the measurements can be made with the same range, great! But if you need different ranges and decide to use auto-range then you cancel out the benefits of hardware handshaking (speed and determinism).

In your case, you want to do multiple temperature measurements but want to use different thermistors/coefficients. NI-DMM does not allow you to do that. The workaround is to simply do your scanning in software timing using single point mode and the NI-SWITCH immediate API.

This may require your program to be multithreaded, which is trivial to do in LabVIEW but may be more challenging in other programming programs. What is the development environment you are using?

[RVallieu]

I suppose I could instead of performing a "thermistor reading" I could simply configure the DMM for scanning 2-wire resistance...

Testing showed that I could get almost the same reading of temp doing it this way and then applying the temperature conversion calculation separately after the acquisition.

It might not be necessary - if they can live with the rate of acquisition at 5 1/2 digits of precision and software timing.

I am programming in LabVIEW.

[santo_13]

sure, you could do a 2-W Resistance measurement across all thermistors (preferably in the same range) and apply the scaling in post processing.

[kirsch]

> Testing showed that I could get almost the same reading of temp doing it this way and then applying the temperature conversion calculation separately after the acquisition.

Yes, this is what the driver does internally anyway. You just opt-out of this ease-of-use feature (automatically doing the temperature conversion math).

> I am programming in LabVIEW.

That helps in the sense that it makes controlling the switch and DMM in their own thread pretty trivial.

> I need a 2-wire switching mode Hardware Scanning Capable NI-Switch to work with a PXI-4071 for measuring Thermistors...

PXIe-4081 would be faster 🙂

[RVallieu]

That requires buying new hardware....