NI 9403 to monitor 12VDC signal

[rjjqwerty]

Hi everyone, 

I have what is probably a basic question to ask about using the NI 9403 DIO module with a cRIO 9038. I want to use a channel on the NI 9403, configured as a DI, to monitor a 12VDC signal coming from a UPS when it is in battery mode. Is this safe to do even though the module is for 5V TTL signals?

The NI 9403 data sheet mentions that there is over-voltage protection Channel-to-COM of +-30V on upto 8 channels at a time.

I am curious to know if anyone has experience on this.

[RTSLVU]

You just need to scale the 12 VDC using a voltage divider,

BTW: Signal conditioning is a major part of data acquisition.

What is Signal Conditioning?

[BertMcMahan]

Note that the datasheet says it's 30 V, but also says:

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±30 V maximum on up to 8 channels at a time;however, continued use at this level willdegrade the life of the module

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For a UPS, if the value is normally 0V and goes to 12V on an error condition that happens infrequently and gets fixed fairly you should be OK. If it's 12V all the time and drops to 0V when there's an issue, I'd worry you'll burn out your module.

Do you have any specs on the output of the UPS? For example, if the output impedance is known, you can sometimes just stick an inline resistor in there and be OK (usually this will be specified in the manual). If you don't have a spec, either create a simple voltage divider like RTSLVU said, or get a card with a larger input voltage range. The inputs of the 9403 have a very high impedance (meaning they will draw only 250 µA max, per the datasheet), so a resistor divider won't load them too much, but the output of your PSU may get loaded more. I'd design a resistor divider to draw no more than 1 mA continuous. In other words- 12 kOhms or higher.

I'd also be ready to shift things around, as you might find voltages don't quite wind up where you want them once you put loads on there.

You could also use a buffer chip. I think this one would work but I've never used it myself; this would require a couple power supplies though (maybe you could use the 12V signal itself?)

https://www.ezsbc.com/product/ls2/

[rjjqwerty]

Hi, thanks for both the detailed responses.  

In terms of specs of the UPS output, I don't have any info on that. From looking at their manuals, all they seem to mention is that there is a RS-232 standard interface port on the backside of the UPS with a 9-pin female D-sub connector. I need to monitor the voltage between two of those pins in order to know when the AC input to the UPS has failed. 

In terms of using a voltage divider or a signal conditioner, I am thinking of using one of these from Phoenix Contact: https://www.phoenixcontact.com/online/portal/us?uri=pxc-oc-itemdetail:pid=2902040&library=usen&tab=1...

Would this work?

It looks like I can set different voltage inputs and voltage outputs using dip switches (I could set the input to 0V - 24VDC and the output to 0V - 5V). I don't know if the other parameters like the input resistance of the voltage input (given to be > 1000 kohms), load/output load voltage output (given to be >= 10kohms) will satisfy.       

Thanks again.

[GerdW]

Hi rjj,

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@rjjqwerty wrote:

In terms of using a voltage divider or a signal conditioner, I am thinking of using one of these from Phoenix Contact: https://www.phoenixcontact.com/online/portal/us?uri=pxc-oc-itemdetail:pid=2902040&library=usen&tab=1...

Would this work?

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Well, yes.

This PhoenixContact converter has the advantage of providing electrical isolation of its inputs and outputs (but needs it's own power supply).

When this is not required I would use two simple resistors or a combination of resistor + z-diode to get the same result…

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@rjjqwerty wrote:

From looking at their manuals, all they seem to mention is that there is a RS-232 standard interface port on the backside of the UPS with a 9-pin female D-sub connector. I need to monitor the voltage between two of those pins in order to know when the AC input to the UPS has failed. 

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A "standard RS232 interface" usually does not provide a "voltage between two pins" (atleast in the sense of determining AC status of the UPS). Why don't you attach the manual or a link to  such a PDF?

[rjjqwerty]

Thanks for the reply. 

Sure, attached is the manual. Refer to page 12 of the manual, which refers to the RS 232 standard interface port. Also, see below snippet. From what was told to me from their customer support, I'd have to monitor the voltage between pin 6 (AC fail output) and pin 5 (common).

[GerdW]

Hi rjj,

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@rjjqwerty wrote:

Sure, attached is the manual. Refer to page 12 of the manual, which refers to the RS 232 standard interface port.

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So they are using a DSub9 connector, but surely not the standard RS232 interface!

I guess I still would use a simple voltage divider from two resistors (or just one adjustable resistor) to monitor that output…

[rjjqwerty]

I see your point, it's not a standard RS232 interface port.

Thanks for the quick responses, really appreciate it. 

Since this is going inside a control enclosure, I'd rather have the DIN rail mountable signal conditioner than using a simpler voltage divider. 

I will explore both though, just out of a sense of curiosity.

Thanks again.

[BertMcMahan]

That looks like it is the Data Set Ready line. You can probably monitor that with an RS232 adapter. It would be much simpler than using a 9403.

[rjjqwerty]

Can you pls give me an example of an RS 232 adapter?

I am not buying a 9403 for this purpose alone. I already use a 9403 for other digital inputs and output with a cRIO 9038 and was trying to use an existing spare channel for this purpose.