Current Loop Proportional Trimmable Circuit

[Rusty789]

This is my first post here, so hello as well! I'm an electronics engineer on paper but haven't really done circuit design since college, so this at the moment is well out of my comfort zone!

The fuel and temperature circuits on my car (Classic Mini) are, I assume (I'm checking it in work tomorrow) driven by a current loop, I've changed the gauges and the scales do not match up (It's not just a case of the scales physically being wrong), so I need a circuit that can take one current loop and give a proportional trimmable output, basically user settable.

Possible?

I'm assuming I need some form of Op-amp circuit, but it's beyond me (well probably not) but I haven't done this kind of thing since college!

 

[Harald Kapp]

Welcome to electronicspoint.

the scales do not match up

Gauge indictaes more than the currents lets you expect?
Easy solution: use a resistor in parallel to the gauge to divert part of the current. Less current will flow through the gauge and the gauge will indicate proportionally less.

Gauge indicates less than the current lets you expect?
Not so easy solution. You will need an active circuit that amplifies the current.

Of which type is your problem?

 

[Rusty789]

Gauge is reading too high, placing a resistor inline will not allow me to set the zero as such though will it? It will just reduce the span overall?

I guess I could try and get it working in work with a potentiometer inline so the max scale reads correctly and just hope the zero tallies up...

 

[Harald Kapp]

placing a resistor inline

Not inline, in parallel. That's a current divider. You want less current through the gauge for any given sensor status.

You should not have to worry about zero because 0 current is 0 regardless of a parallel resistor.