Question 54 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is A. **Explanation for Option A (Correct):** Option A is correct because when a digital multimeter (DMM) is specifically set up to test capacitance (typically denoted by a symbol like $\text{nF}$ or $\mu\text{F}$ on the function dial, often corresponding to figure "B" showing the leads across a capacitor in a capacitance testing mode), the meter performs an internal measurement—usually by charging and discharging the capacitor and measuring the time constant—and displays the actual capacitance value. If the capacitor is functioning properly, the displayed value will be the measured capacitance, which must fall within the tolerance range specified by the manufacturer (e.g., $100 \mu\text{F} \pm 10\%$). **Explanation of Incorrect Options:** * **B) initially a very high ohmic value will be displayed (OL ohms), followed by a gradual drop in resistance until a very low value is displayed:** This description refers to how an analog multimeter (VOM) set to the **resistance (Ohms) function** (using an internal battery to charge the capacitor) would test a capacitor. The initial high resistance is the open circuit, and as the capacitor charges through the meter, the resistance appears to drop. This is a resistance measurement, not a direct capacitance measurement, and is generally not how a modern DMM in capacitance mode operates. * **C) the charging voltage would be displayed which will initially be low and gradually rise to the internal battery voltage:** This would occur if the meter was set to the **DC Voltage (VDC) function** while measuring the voltage across a capacitor being charged by an external source. It does not describe the result of a dedicated capacitance test (Figure B). * **D) initially a very low ohmic value will be displayed, followed by a gradual rise in resistance until a very high value is displayed (OL ohms):** This is the standard procedure and reading for testing a functioning capacitor using a digital multimeter set to the **resistance (Ohms) function**. The low value is the initial charging current (appears low resistance), and as the capacitor charges fully, the meter reads "Open Loop" (OL), indicating infinite resistance. While this is a valid functional test, it measures resistance over time, not the actual capacitance value, which is what a dedicated capacitance function (as implied by the setup in Figure B for a modern DMM) is designed to display.