Re: Low Current Measurement (without ammeter)
- From: "John O'Flaherty" <quiasmox@xxxxxxxxx>
- Date: 27 Jul 2006 07:39:47 -0700
ewilliams2@xxxxxxxxx wrote:
Hello Everyone,
I have an application that uses 3 displacement sensors with analog
current output from 0 to 20mA. I have a real time DAQ system that only
measures voltage from 0 to 10V. I have read the previous response to
Pradheep's question and it seems like the current values are too high
to get the kind of precision that I need. I was wondering if I could
use the resistor in series method and if there was some trick that
could help me develop this setup? Any help at all would be appreciated,
because I've never had to measure currents like this before so I'm a
little beside myself trying to figure this one out...Also if the
resistor "shunt" is placed in series what kind of accuracy can be
achieved?
If you put the current into an opamp inverting input, with a 500 ohm
feedback resistor, and the non-inverting input grounded, it will
convert 0-20mA to 0 to -10V, and the output will be stiff even if it's
loaded a little. You'd have to invert the output to +10 V. If the opamp
needs to be protected from voltages, you can use a series resistor with
diodes to plus and minus supply on the opamp input to limit voltage
excursion, but you'd have to make sure the current source has enough
compliance to handle the extra resistance. The source will only need
enough voltage compliance to handle the drop across that protective
resistance.You could also just use a 500 ohm resistor, if the DAQ
system has high input impedance. Using just a 500 ohm resistor, the
current source would have to have the compliance to produce the 10V.
--
john
.
- Follow-Ups:
- Re: Low Current Measurement (without ammeter)
- From: ewilliams2
- Re: Low Current Measurement (without ammeter)
- References:
- Low Current Measurement (without ammeter)
- From: ewilliams2
- Low Current Measurement (without ammeter)
- Prev by Date: Re: Just checking in
- Next by Date: Re: Low Current Measurement (without ammeter)
- Previous by thread: Low Current Measurement (without ammeter)
- Next by thread: Re: Low Current Measurement (without ammeter)
- Index(es):
Relevant Pages
|
