How accurate is the ADC on PIC18?

[chris414]

How much accuracy can I expect with a PIC18F2550? I'm using the example code from microchip for some simple ADC and compared with my multimeter (it's a good multimeter, not a cheap supermarket special) it's reading about 0.2V higher than the actual reading (the error is less at lower voltages). Is this normal?

 

[eng1]

How much accuracy can I expect with a PIC18F2550? I'm using the example code from microchip for some simple ADC and compared with my multimeter (it's a good multimeter, not a cheap supermarket special) it's reading about 0.2V higher than the actual reading (the error is less at lower voltages). Is this normal?

How good is your reference voltage? Did you choose Vdd as the reference for the ADC or are you using a precise external reference?
What is the source feeding the ADC?

 

[Oznog]

Assuming you used a voltage divider, the divider resistors' accuracy makes an enormous difference. As much as +5% on one and -5% on the other (worst case) is a lot of error!

The PIC18F's ADC is just as accurate as the spec sheet (and errata sheet) says.

 

[spindrah]

How much accuracy can I expect with a PIC18F2550? I'm using the example code from microchip for some simple ADC and compared with my multimeter (it's a good multimeter, not a cheap supermarket special) it's reading about 0.2V higher than the actual reading (the error is less at lower voltages). Is this normal?

if you had it set up right you should be within 0.01volts of actual