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6220 giving odd signals. Could it be broken?



I am using a 6220 on a SCXI 1000 with a 1302 board. This means that I essentially have the 6220 board liked to a pinout.


The issue I am having is that the board is not responding to input signals anymore. I have a 10VDC power supply to two pressure sensors and the maximum voltage out is 5 volts. The board is rated to 11 volts, so I do not believe that the board could be destroyed. Every time I connected and disconnected the board I shut down the SCXI unit.


At first I noticed that the singals were climbing or falling from the two pressure sensors. They would give a solid signal, but in the course of 10 minutes the pressure readout would change by +-40kpa. The signal would waver in a range of 1-4kpa as a result of noise. As well, there were rouge jumps. Sometimes the signal would jump 100 kpa, remain at that readout for a second, then fall to its original value.


My first plan was to redo the grounding on the unit. I attached the - line from the 10VDC power supply to the ground. I checked the voltages and found the difference to be 5VDC between the ground and +, and 10mV between ground and -. I connected it to the board and was at first happy with the stable signal, but then one line didn't respond to changes in pressure. Then the other line didn't respond. There was an output signal which was entirely independent of the pressure readout. The output was magnitudes larger than what was really happening.


I have also done the following tests

1. After testing various sources of noise, I disconnected the cable to the 6220 and found the same signal was occurring in high magnitudes even without an input.

2. The other boards on the SCXI are working and responding to input signals, but they have similar massive jump which remain up for a second before dropping down. At the top of the jump the signal is relativity smooth and looks the same as the signal from the bottom, just increased.

3. I changed the grounding so that the - line from the pressure sensor output was connected to ground. There was no change in output signal

4. I disconnected both the - line from the pressure sensor and the - line from the power supply from the ground. This resulted in the output signal climbing or falling. The signal would climb or fall for several seconds before staying around 8.5 V. The signal did not change as a result of pressure change.


I do not know what is the cause of the ai0,ai1,ai2,ai3 and so on channels on the 6220 board. Any suggestions of why or how I can fix this?



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I have also been doing some more testing. The board is responding to a signal, but not the input signal


When I disconnected the pinout board to the 1302 and put it back into the scxi 1000 unit, I monitored the output from ai0 in the M&EA window as the power was turned on. The voltage reading which had been about -1.4V approached -8.54V before remaining in that range. The voltage did not change as a result of change in input. I turned off the scxi 1000 and the voltage returned to -1.4V with the same noise as the signal at -8.54 after a rapid then slower approach to the final value. 


So there is input, but I do not know why the 6220 board is

A. Not reading any change in my input

B. 8.54V since the maximum voltage difference on the 1302 test panel is 5V


Any ideas would be helpful. I will be getting an oscilloscope tomorrow to test the input signals more thoroughly.

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 If you supply a known voltage from a battery/power supply to the input channels, do you observe correct readings?


Best regards,


Ali M

Applications Engineer

National Instruments

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I found out half of my problems, but I have a long way to go. My problem was I had the negative voltage from the power supply was connected to the negative input and the negative signals were connected to the ground. Now I am trying to figure out this drifting issue. Pressure Sensor 1 is linked to AI0 and AI7. Pressure Sensor 2 is linked to AI2 and AI8


I connected a voltmeter and measured the voltage on the two pressure sensors I have


Pressure Sensor 1 = 00.0mV

Pressure Sensor 2 = 00.4mV


The pressure sensors go up to 100psi and have 3mV/m rating


I connected a air hose up to the output of the pressure sensors and sucked on the end


Pressure Sensor 1 = 02.7mV

Pressure Sensor 2 = 03.1mV


The voltage did not drift, shift or change


When I am looking at a readout in the M&AE, I see the voltage is as follows. The voltage readout then approaches the second value after 40 minutes. Even then, the readout drifts over time.


Pressure Sensor 1 = 0.1286V goes to 0.1767V

Pressure Sensor 2 = 0.3317V goes to 0.3132V


When I suck on the end of the lines, the voltage does increase and then decrease accordingly.


When I turn off the SCXI-1000, the voltage has spikes and the readout changes.

After SCXI-1000 is turned off the voltage changes to voltages in the 1.0e-7V. When I disconnect the SCXI-1302 from the SCXI-1000, the voltage goes to 2.5V


My current problem is this drift. I do not know why or how the drift occurs.

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I have found the source and the solution to my problem


When I had first set up the pressure sensors I had set them up as a Custom Voltage With Excitation. This was a mistake. The reason I had selected Custom Voltage with Excitation was because I had this setup left over from my first setup with reading the input on the SCXI-1124 (I think) board which had an internal power source. I changed this to Measure Voltage. Now I am reading proper values of voltage instead of what I had before


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