9225 AC voltage reading

[TomasBG]

Hi, I am trying to design an equipment, that needs to read Vac and Vdc.

However my question is the following, they willl be plugging and unplugging the connectors in NI9225 often.

If they make a connection mistake let's say flip and connect AI0- in AI0+. and vice-versa. Will I be able to detect the fault?

My way of seeing is that it won't detect it since it's Vrms, and will read Positive when it's Vac since it's reading the Vrms value..

thanks!

[Henrik_Volkers]

the NI9225 will always read a 'short time DC' value, the 300Vrms spec just give you a hint for the max voltages to be applied. There is no (true) rms converter involved. If you want to measure the rms value you have to measure at least exactly one periode of your AC signal with an appropriate samplerate and do the rms calculation by yourself. (OK, let LabVIEW do it 😉 )

If you deal with voltages higher than 50V you should make serious thougths about the persons who do the connections!!

If you have a pure AC signal (no DC offfset) and no phase information, it will be hard to detect a swapped AC connection. But if you have two channels with an AC signal and have an educated guess of the what you expect to measure (say power consumption of a load) the phase relation can give a hint of swapped inputs.

You can't make a system fool proofe, fools are to creative 😄

Think about adding additional connectors that are more robust.

[TomasBG]

Yeah, the problem is that I have to make it fool proof, this is for a test equipment

The input voltage will be 230VAC.

Ideally I was thinking on using.

AI0+ for Line Cable

AI0- for Neutral Cable

However with what you mention I am thinking on proceeding the following way:

AI0+ for Line Cable

AI0- to GND

then use the next channel as the following:

AI1+ for Neutral Cable

AI1- to GND

Do you think that will work? I mean if they connect Neutral to Line and Line to Neutral, I think I will be able to identify it since. AI0+ will read 230 VAC, while AI1+ will read 0 or GND.

even I can change AI1 instead of using GND place a reference Neutral line to compare. if discrepancy is less than let's say 10% then it's cool.

What do you think?

[Henrik_Volkers]

I would use one input pair to measure L-N , because thats the value of interest.

Another pair to measure N-PE  to detect a swapped AC line.

Think about hard wired PE to the system ...  

Again: Think of adding another plug/socket for the test setup .. a worn out socket is cheaper than a 9225 repair 😉  Harting (to name one) makes nice robust connectors. Have you seen screw connectors after 200 reconnections? (With and without using torque restricted screw drivers?)  

You can do a lot of stuff in a controlled laboratory...  but this sounds more like a end of line test on the floor. So I recommend to search someone who really knows the standards (in Germany VDE, BGV ... and many more)  ... and your questions already showed that you don't know them! 

[TomasBG]

Oh! The solution of L-N and N-PE is the best one! I like it!

Trust me I would add a socket  if I could, but the issue is that the assembly doesn't include a socket, so there is alot of room for mistake. The wires are identified but if they plug the wrong cable then.. there's nothing I can do to prevent it (except following your solution).

And yes this is more as in Production Assembly Test, in which sadly, said assembly was not designed for testing.

They are three pair of cables that need to be tested.

Two with 200 Vdc that drop to 110 Vdc after 5 sec.

and this 3 cables ( N, L, PE)  230Vac

My idea was to connect one per channel, but now I guess I will use a relay to alternate one channel.

And yeah I don't have much experience with standards, can you submit some links? I am more interested in North America Standards..

Best regards,