troubleshooting usb 6211

[kaiopaka]

Hi,

In our lab, we use a usb 6211 to generate a 0-10V signal that controls a variable power microwave.  Recently, we've been having trouble with the microwave turning on and off rapidly at an input signal of 1V (but not higher, then it is stable).  I was wondering if anyone had any tips for trouble shooting the 6211 so I can track down the problem, and see if it is the 6211 or if it is the pc board of my microwave.

KaiOpaka

[micahmcc]

Hi KaiOpaka,

I think some more information regarding your setup and the microwave will help us understand the issue better. Here are some quick questions:

• Can you give us more info about your control signal? (Analog/digital, frequency, waveform, etc.)
• What is the on/off thresholds for your microwave? (perhaps it's off-on threshold is right at 1V and therefore the slight variations cause it to switch rapidly)
• Was the microwave working with a 1V signal before? If so, what has changed?

If I were troubleshooting, I would verify the output of my 6211 with an oscilloscope to make sure the signal is good. I would also use a DC output and slowly increase/decrease it to see if there is a certain value that makes it turn on/off rapidly. Basically, I would start by giving the microwave a known control signal to see how it behaves then I would move on to testing your 6211 itself.

But like I said before, more information on your setup and what is happening as opposed to what should be happening will be very helpful in providing troubleshooting steps. Feel free to post back when you get the information and I'll give it another look!

[kaiopaka]

Thank you for your kind reply.

My control signal is DC, I think analog (I didn't set up the system, I'm just maintaining it).  Essentially, we type into the VI the power we want from the microwave (from 300W to 3000W) and the USB 6211 signals the power generator to turn on and provide that power. The remote control chip in the microwave interprets a 1V to10V trigger into 300W to 3000W output power. Currently what is happening is rapid, variable power (ranging either off or between 300W to 1000W) when asked for 300W.  From 310W to 3000W, we get steady power.   The on-off threshold is right at 1V, but it has never done this before (the microwave is over 18mo old), which is why I'm starting with either the signal from the USB 6211 or the pc chip inside the microwave's interperetation of that signal as the culprit.   

I will start with the suggestions you already made as soon as I can find an o-scope to borrow. 

KaiOpaka

[micahmcc]

Ah, I understand the problem better now. Thank you for the extra info!

I would still stick to the original plan of measuring the control signal of the 6211 first to ensure the integrity of the signal. If the signal looks good on the scope, then it is probably the PC board of the microwave (especially if this setup has been working for a long time and you haven't changed anything).

I look forward to hearing how it goes!