zmanvortex
Member
Ok, I am trying to get a 0-20ma or 4-20ma analog input off of a potentiometer into an analog input card.
I want to use the AutomationDirect F0-04AD-1. On the product page it specifically says it is for use with 24VDC power supply.
When I went to the spec page it showed input impedence of 125ohms at 1/8 watt.
Now correct me if I am wrong but 24VDC at 20ma would be almost 1/2 watt. What gives? I called tech support and they said that the 24VDC should be used to power a 0-20ma/4-20ma current generating device that should be limited to 1/8 watt output (which would mean 6.25volts at 20ma). I have a hard time believing that they would specify what voltage should be used to power the current generating device as long as it output the correct values.
What I had planned was using 24vdc with a 2k potentiometer and a 1k current limiting resistor in series with the wiper and the input of the analog card.
This would give me 0-20ma of current over the range of the pot but with the pot turned all the way up would also give 24vdc to the analog input which would result in almost 1/2watt.
I am just finding it hard to believe that it so hard to use a potentiometer with an analog input card.
Thanks.
I want to use the AutomationDirect F0-04AD-1. On the product page it specifically says it is for use with 24VDC power supply.
When I went to the spec page it showed input impedence of 125ohms at 1/8 watt.
Now correct me if I am wrong but 24VDC at 20ma would be almost 1/2 watt. What gives? I called tech support and they said that the 24VDC should be used to power a 0-20ma/4-20ma current generating device that should be limited to 1/8 watt output (which would mean 6.25volts at 20ma). I have a hard time believing that they would specify what voltage should be used to power the current generating device as long as it output the correct values.
What I had planned was using 24vdc with a 2k potentiometer and a 1k current limiting resistor in series with the wiper and the input of the analog card.
This would give me 0-20ma of current over the range of the pot but with the pot turned all the way up would also give 24vdc to the analog input which would result in almost 1/2watt.
I am just finding it hard to believe that it so hard to use a potentiometer with an analog input card.
Thanks.