1. Multi-Range Analog Ammeter
Multiple Full-Scale Values
Ranges less than and/or greater than the device’s full-scale value
Measure 10 mA with a 0-1 mA device
Analog Meter
Moving-pointer
Works by interaction of magnetic fields
ECE 201 Circuit Theory I

2. Basic Analog Meter Movement
ECE 201 Circuit Theory I

3. Interaction of Magnetic Fields Basic DC Motor
Permanent Magnet Magnetic flux from N to S
Current into A and out of B Magnetic flux due to current
ECE 201 Circuit Theory I

4. Resulting CCW Rotation
Flux “Bunching”
Mechanical forces on the conductor
ECE 201 Circuit Theory I

5. Extending the Range of an Ammeter
Meter movements available in standard full-scale values
We have 0 – 1 mA
To measure currents greater than 1 mA, we need to “divert” the extra current away from the meter using a “shunt”
ECE 201 Circuit Theory I

6. Calculation of the Shunt Resistor
Measure ILoad
Ishunt = ILoad - Imeter
Parallel combination of meter and shunt
ImeterRmeter = IshuntRshunt
Rshunt = Rmeter(Imeter/Ishunt)
Need to know Rmeter !
ILoad
Imeter
Ishunt
ECE 201 Circuit Theory I

7. Here’s how NOT to measure the resistance of the meter movement
Do not connect the meter movement to any analog or digital multimeter configured as an ohmmeter!
The internal battery will supply too much current and destroy the movement!
ECE 201 Circuit Theory I

8. Preliminary (Prelab) Work
Devise a non-destructive scheme to determine the internal resistance of the meter movement.
You may use any equipment or components (power supply, function generator, resistors, potentiometers,etc.).
Have your method approved BEFORE you begin the experiment!
ECE 201 Circuit Theory I

9. Calibration of your Meter
Measure the same current with the meter you designed and a “standard” (commercial) meter.
Plot the reading of your meter as a function of the readings obtained with the standard meter.
ECE 201 Circuit Theory I