Posted ByLeon on November 16, 2001 at 13:48:22:
In Reply to: Input impedance of Analog inputs posted byWill White on November 16, 2001 at 10:57:21:
How high is the voltage?
The chip data sheet did not state the input impedance except that the maximum allowable analog signal source impedance is 10 K Ohm and the input capacitance is 20pF. I did a quick measurement using a voltage divider technique and got a measurement for T100MD888+ of about 10 M Ohms impedance for the analog input 1-6.
For T100MD1616+ the measurement show only about 1M Ohms for the input #1 & #2 of T100MD1616+ and even lower value for #3 & #4.
You may want to consider adding a unity gain buffer using a high input impedance opAmp such as the LT1014 which purportedly have input impedance of 300M Ohms before connecting to the T100MD's input.
: Hello! I need to know the input impedance to the analog inputs. I am trying to interface a high voltage probe to the PLC's analog input and the probe needs to see a 10 MOhm impedance to properly measure the voltage (it is really just a compact voltage divider). I have tried measuring the input impedance to analog input 1 and come up with a value of about 330 kOhms. Is this correct?
: Thanks,
: Will