Every inline series-connected ammeter, including a multimeter in a current range, has a certain resistance. Most multimeters inherently measure voltage, and pass a current to be measured through a shunt resistance, measuring the voltage developed across it.
In general, stick to DC circuits (the settings on the multimeter with straight lines, not curvy lines). Most multimeters can measure AC (alternating current) systems, but AC circuits can be dangerous. A wall outlet with AC or 'main voltage' is the stuff that can zap you pretty good.
Electric potential is electric potential energy per unit charge, measured in joules per coulomb (volts). "Electric potential" must be distinguished from "electric potential energy" by noting that the "potential" is a "per-unit-charge" quantity.
Electrical resistance is measured by either of two methods: constant current or constant voltage. The constant current technique sources a known current through an unknown resistance and the resulting voltage is measured. This technique is generally used for resistance values below 200M ohms.
Turn power to circuit OFF. If a circuit includes a capacitor, discharge the capacitor before taking any resistance reading. 2. Turn dial to Ω (resistance, or ohms), which often shares a spot on the dial with one or more other test/measurement modes (continuity, capacitance or diode; see illustration below).
Resistance on your electronic circuit is measured in ohms, represented by the Greek letter Omega (Ω). Measuring resistances is similar to measuring voltages, with a key difference: You must first disconnect all voltage sources from the circuit whose resistance you want to measure.
Voltage is meaured using a voltmeter. Some types of voltmeter have a pointer on a dial, but most have a digital readout. To measure the voltage across a component in a circuit, you must connect the voltmeter in parallel with it. You can measure the voltage across a cell or battery.
Step 13 Testing Resistance
- To begin, make sure no current is running through the circuit or component you want to test. Switch it off, unplug it from the wall, and remove any batteries.
- Plug the black probe into the COM port on your multimeter.
- Plug the red probe into the VΩmA port.
Set your multimeter to the highest resistance range available. The resistance function is usually denoted by the unit symbol for resistance: the Greek letter omega (Ω), or sometimes by the word “ohms.” Touch the two test probes of your meter together. When you do, the meter should register 0 ohms of resistance.
- Always test your meter first!
- Determine the amperage rating for your digital multimeter.
- Select the appropriate function on your multimeter.
- Set the range on your multimeter.
- Plug the leads into the appropriate terminals.
- Run the circuit through the multimeter to measure the current.
Method 1 Measuring Resistance with a Digital Multimeter
- Choose the item whose resistance you wish to measure.
- Plug the test leads into the correct test sockets.
- Turn on the multimeter and select the best testing range.
- Touch the multimeter leads to the ends of the component you are testing.
- Turn off the multimeter.
A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.
Step 3: Use Ohm's law to calculate the voltage across each resistor:
- identify formula(using the triangle): V = I x R.
- insert numbers for resistor 1: V1 volts = 0.5A x 1Ω = 0.5 Volts.
- insert numbers for resistor 2: V2 volts = 0.5A x 4Ω = 2.0 Volts.
To measure ac/dc current with a voltage output clamp, turn the dial to mVac for ac current, or to mVdc for dc current. Plug the black test lead into the COM jack. For plug-in clamp accessories that produce a voltage output, plug the red test lead into the V jack.
Current (I) – is measured in amperes (A). Current is the rate of flow of charge. A current of 1 A means that 1 coulomb of charge flows past a point in a circuit every second. ( 1 A = 1 C s-1 ) Current is measured in a circuit using an ammeter which is placed in series with the component of interest in the circuit.
A constant current is passed through the resistance under test and the digital multimeter measures the resulting voltage across the resistance as shown in the following figure. With a known current source and measured voltage, the digital multimeter can determine resistance using Ohm's Law VM = Is *R.
Emf and Internal Resistance. Incidentally, a pure voltage source is usually referred to as an emf (which stands for electromotive force). Of course, emf is measured in units of volts. A battery can be modeled as an emf connected in series with a resistor , which represents its internal resistance.
The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.
How to test for continuity
- Turn the dial to Continuity Test mode ( ).
- If required, press the continuity button.
- First insert the black test lead into the COM jack.
- Then insert the red lead into the V Ω jack.
- With the circuit de-energized, connect the test leads across the component being tested.