reading ADC problem

[Alan]

My hardware is a T100MD-1616+ r44

ADC1,2, and 4 are functioning properly, that is, I can apply a voltage to the input and read the bits in the "Online Monitor" and from my Modbus driver.  However ADC3 does not change its' status when a voltage is applied, it remains at a constant +-680 bits.  ADC1,2&4 will also go to 0 when grounded.  ADC3 will not.


My dCusF is as follows:

FOR K = 1 to 4 STEP 1
      DM[K] = ADC(K)
NEXT

'DM[1] = ADC(1)
'DM[2] = ADC(2)
'DM[3] = ADC(3)
'DM[4] = ADC(4)

This CusF runs once a second.


What could be the problem?

Alan

[support]

I assume you have observed the value of ADC #3 and DM[3] on the on-line monitoring -> view varaible screen? If they are stucked ON at around 680 that means the ADC #3 input may be a problem. When you apply voltage to ADC #3, did you use a voltage meter to measure the applied voltage and get a correct voltage reading? If you trace the PCB connection you should find that the ADC #3 is connected to the CPU via a series-connected resistor. You may want to measure the applied voltage before and after the resistor to see if the connection from the screw terminal to ADC is good. If all else failed, please contact us or the distributor to arrange for a replacement.

[Alan]

Yes, I have verified the stuck ADC3 reading in both the Online Monitor and View Variables DM[n] screens.  I traced the PCB connections and read the input voltage before and after the resistor you mention, the value is the same on the input side and output side of the resistor.  There is a good connection between the screw terminal and the resistor.

I'll contact you tomorrow about replacement.


Thanks,

Alan