Internet PLC Forum

General => Technical support => Topic started by: Bill Alexander on August 10, 2006, 10:25:04 AM

Title: Analog input problems
Post by: Bill Alexander on August 10, 2006, 10:25:04 AM

I am communicating a 0-5 V signal to A/D #1 on aT100MX+ and I am having problems.  I have the signal being read when a brake is pressed, but it always comes out 4092.  I do have 5V reference voltage and grounding.  Also, when testing the voltage after the analog port, the line voltage has been knocked down from 3V to .6V as an example.  Any ideas on what's going wrong?

Thanks!

Title: Re:Analog input problems
Post by: support on August 10, 2006, 11:19:31 AM

Make sure that you are connecting to ADC #1 (which is pin 8 on the DB15) and not ADC #8 (which is pin 1 on the DB15).

What is "after analog port"? Do you mean you measure on the ADC terminal after connecting it to the DB15 connector? There is no reason for the drop since the ADC input impedance is > 1 M ohms. Make sure that you have a stable +5V analog reference voltage to power your sensor as well as connect to the analog reference voltage of T100MX+. Note that T100MX+ does not generate the 5V reference (unlike on the T100MD+) so you need external analog reference voltage.