rrd Posted January 18, 2007 Report Share Posted January 18, 2007 I am working on a sensor array- 6 sensors. I have connected the array through amp circuitry to SCB 68 box. I expect the MAX to give readings of sensor values. All i got was a noisy waveform on the MAX display. i used a multimeter to measure sensor outputs and detected an average of 1.5- 2 V, that was before a gain 2 amplification. The readings on the sensor seem not to affect the reading of MAX test, as same reading continues after signals were disconnected. What result should a MAX test panel give? Mine showed some continuously varying value until it stopped at around 10.8 V. I have just got DIAGNOSTIC Tool 2.0 to test the board and it indicated all is well: all PASSES. What then may be wrong ? Quote Link to comment
Guillaume Lessard Posted January 18, 2007 Report Share Posted January 18, 2007 If disconnecting the signals doesn't change anything, maybe they weren't connected to begin with. That really is what your description sounds like. (I've done it many times, and was dismayed every time...) Check all your connections. Make sure you're connecting to the right pins. Make sure you amps are sufficiently powered. Quote Link to comment
Chris Davis Posted January 18, 2007 Report Share Posted January 18, 2007 Are your signals differential or (referenced) single ended, from what you describe, it sounds like your ground is not present and the card is going into its default noisy sine wave mode Quote Link to comment
rrd Posted January 19, 2007 Author Report Share Posted January 19, 2007 Are your signals differential or (referenced) single ended, from what you describe, it sounds like your ground is not present and the card is going into its default noisy sine wave mode I guess that too. Today i tried what i got from the SCB 68 manuals for differial input. I connected a small 9V battery and place a 100ohms resistor acros a specified place on the PCB of the SCB 68. It was able to record the voltage as expected. However all the channels indicted values close to 9.1 V. I expect only the channel with the battery to record this. Quote Link to comment
AnalogKid2DigitalMan Posted January 19, 2007 Report Share Posted January 19, 2007 I guess that too.Today i tried what i got from the SCB 68 manuals for differial input. I connected a small 9V battery and place a 100ohms resistor acros a specified place on the PCB of the SCB 68. It was able to record the voltage as expected. However all the channels indicted values close to 9.1 V. I expect only the channel with the battery to record this. If the other channels are not connected to anything, their readings will tend to 'float' around the values of adjacent channel(s). This is due to the high input impedance on the front end of the analog to digital converter and the inherent capacitance of the input stage. The capacitance charges up and holds the voltage since there is hardly any path for it to discharge into. Quote Link to comment
rrd Posted January 19, 2007 Author Report Share Posted January 19, 2007 If the other channels are not connected to anything, their readings will tend to 'float' around the values of adjacent channel(s). This is due to the high input impedance on the front end of the analog to digital converter and the inherent capacitance of the input stage. The capacitance charges up and holds the voltage since there is hardly any path for it to discharge into. Thank you for that information. So how do i prevent this other channels' 'float' around the values of adjacent channel(s) ?. Quote Link to comment
JDave Posted January 19, 2007 Report Share Posted January 19, 2007 Thank you for that information. So how do i prevent this other channels' 'float' around the values of adjacent channel(s) ?. Just tie all the channels you are not using to ground. Quote Link to comment
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