Hi all
I'm hoping for a bit of help with the circuit shown.
Its 23 years since I last studied op amp circuits and the old grey matter going a bit soft so I hope you can help.
The circuit is part of a control system for positioning a hydraulic ram. R3 and R4 are trimmers to set max and min up/down position of the ram designed to be set to R3=10 ohm & R4=25 ohm. The control variable resistor is moved by a lever the operator moves, the sensor variable resistor (identical to the control one, both 5 to 190 ohm) is mechanically linked to the ram and provides position feedback to the circuit. The output of the circuit is supposed to vary between 0.4 and 5v. The output is supposed to be 2.5v when both variable resistors are in the same position and the ram is motionless. The output is fed into some comparitor circuits that produce up/down signals to move the ram, this bit of the circuit I understand. It's this bit of the circuit I can't analyse properly.
How I see it at the moment is (and I am probably wrong):
It's some sort of differential amplifier.
Gain is R1/R2 = about 3
The voltages at points A & B are basically set by the resistor chains, which act as voltage dividers.
The control variable resistor varies voltage B from 1.66 to 2.5v.
The Sensor variable resistor varies voltage A from 2.5 to 1.25v.
There are a few capacitors but this is basically a DC circuit.
Any help in analysing / understanding this better or anyone seen the same circuit used elsewhere gratefully appreciated.
(sorry about the diagram quality)
prh
I'm hoping for a bit of help with the circuit shown.
Its 23 years since I last studied op amp circuits and the old grey matter going a bit soft so I hope you can help.
The circuit is part of a control system for positioning a hydraulic ram. R3 and R4 are trimmers to set max and min up/down position of the ram designed to be set to R3=10 ohm & R4=25 ohm. The control variable resistor is moved by a lever the operator moves, the sensor variable resistor (identical to the control one, both 5 to 190 ohm) is mechanically linked to the ram and provides position feedback to the circuit. The output of the circuit is supposed to vary between 0.4 and 5v. The output is supposed to be 2.5v when both variable resistors are in the same position and the ram is motionless. The output is fed into some comparitor circuits that produce up/down signals to move the ram, this bit of the circuit I understand. It's this bit of the circuit I can't analyse properly.
How I see it at the moment is (and I am probably wrong):
It's some sort of differential amplifier.
Gain is R1/R2 = about 3
The voltages at points A & B are basically set by the resistor chains, which act as voltage dividers.
The control variable resistor varies voltage B from 1.66 to 2.5v.
The Sensor variable resistor varies voltage A from 2.5 to 1.25v.
There are a few capacitors but this is basically a DC circuit.
Any help in analysing / understanding this better or anyone seen the same circuit used elsewhere gratefully appreciated.
(sorry about the diagram quality)
prh