# Multi-Range Simple Ammeter - PowerPoint PPT Presentation  Multi-Range Simple Ammeter

## Multi-Range Simple Ammeter

##### Presentation Transcript

1. Multi-Range Analog Ammeter • Multi-Range • 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 FieldsBasic DC Motor Permanent Magnet Magnetic flux from N to S Current into A and out of BMagnetic 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