Overclocked
Member
I want to build a 4-20mA loop calibrator for work. Ive decided it will be powered by a battery (9V) but can also be loop powered to withstand up to 30V. I originally looked into using a LM317 as a constant current source, But 1) I am worried about accuracy and 2) The resistors I would need are hard to get (62 Ohms and 312 Ohms) in the accuracy I would want them, so Ive decided to build a Constant Current source using a op-amp. I would like the calibrator to be accurate to atleast 0.03% or better, since the A/D converters that are used use 15 bits. Ideally I would like each box to cost $5 to $10 each.
What would I need to look for in a Op-Amp that's to be used as constant current source? I would use a Zener diode 0r Voltage reference that is atleast accurate, or more accurate than I need. Resistors would have to be 0.1% Tolerance or better.
Or does any one have suggestions for LDO's that will be just as accurate?
What would I need to look for in a Op-Amp that's to be used as constant current source? I would use a Zener diode 0r Voltage reference that is atleast accurate, or more accurate than I need. Resistors would have to be 0.1% Tolerance or better.
Or does any one have suggestions for LDO's that will be just as accurate?