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Extracted text: ww. Im Ry E R1 digital Figure 2 Since the beth resistors Rm and Rah are connected in parallel, then the voltage across them is the same. As a result, we can write the folkowing RIn = R(I - I.) (1) where Im is the current passing through the galvnnometer and I is the current to be measured. By r-arranging 1, we get the following R,A = (2) T- im 3 Tools and Components 1. A power supply 2. Varinhle resistors. 3. A galvanemeter. 4. A digital multimeter. 5. Wires. 4 Procedure 4.1 Measuring the internal resistance R 1. Select a variahle resistor Ry. Set its value to maximum (use the digital ohmmeter). 2. Conneet the circuit shown in Figure 2. Set the source at 2 volts and (R - 1000). 3. Reduce the value of R, until the galvanometer reads full-scale current. 4. Take the value of i from the digital ammeter and use to caleulate the fellowing R(1 - Im) Rm = (3) 2 ww. Im Ry E R2 digital Figure 3 4.2 Increasing the range 1. Set the resistor R, value to maximum (use the digital ohmmeter). 2. Calculate the shunt resistor R2 to be connected to the galvanometer to increase its range to (1.6.4) using the following R, = . (4) !- I. 3. Conneet the cirenit shown in Figure 3. Set the power supply at 2 v 4. Reduce R. util the digital ammeter reads (0.84)- Takke the reading of galvanameter (the pointer shouki be elose to the middle of range). 5. Increase R, until the digital anmeter reads (1.2A). Take the reading of the galvanometer. 5 Discussion 1. Discuss the results cheained in Section 4.2. 2. How can we inerease the range to 1A? 3. Why is the ammeter always comnected in series with any cirenit? ww
Extracted text: Experiment no. 3: Increasing The Range of an Analog Ammeter Prepared by: Dr. Ali Al-Hashimi Department of Medical Instrumentation Techniques Engineering Al-Amarah University College 1 Objective .. The objective af this experiment is to understand how to ccnvert a galivanometer (a PMMC am: into an ammeter with a higher Tange. 2 Introduction Galvanometer is a PMMC analog sensitive device that is used to detect very low currents (in the order of mieroamperes). Its working principle is based on the electromagnetic induction. More specifically, A coil placed in a uniform magnetike fiekl experiences a torque when an electric current is set up in it. The deflection of the coil is determined by a pointer attached te it, maving on a seale. As mentioned above, the galvanometer is a sensitive device which ean detect the presece of very small eurrents in a cireuit of the order of milliamperes to mieroamperes. For measuring currents with higher values, a low resistance called shunt resistance (R) is connected in parallel across the galvanometer having an internal resistance (). Figure 1 shows a model of a galvanometer. 100 O 200 100 G 200 GALVANOMETER Figure 1 www Im Ry E R1 digital Figure 2 Since the beth resistors Rm and Rah are connected in parallel, then tbe voltage acroes them is the same. As a result, we can write the folkowing RIm = R(I - .) (1) where In is the current passing through the galvanometer and I is the current to be measured. By re-arranging 1, we get the following R.A = T- Im (2) 3 Tools and Components 1. A power supply 2. Variable resistors. 3. A galvanometer. 4. A digital multimeter.