# MULTIMETER

## WHAT IS A MULTIMETER?

Sometimes also called multimeter or tester, it is a measuring instrument that offers the possibility of measuring different electrical parameters and magnitudes in the same device. The most common electrical parameters are those of voltmeter, ammeter and ohmmeter.

The measurements can be made for continuous or alternative current at several measurement scales each. The latest analog and later have been introduced in digital devices with the function of it, with an added variant.

• An ideal voltmeter has infinite input resistance and does not draw current.
• An ideal ammeter has zero input resistance and has no voltage drop across it.

Unfortunately, real sources and meters have terminal characteristics that are a bit different from the ideal cases. However, the terminal characteristics of the actual sources and meters can be modeled using ideal sources and meters with their associated input and output resistors.

## DIFFERENT COMMON FUNCTIONS IN MULTIMETERS:

### RESISTANCE MEASUREMENT

To avid electric shock personal injury or damage to the meter, disconnect power to the circuit and discharge all high-voltage capacitors before testing resistance, continuity, diodes or capacitance.

### CONTINUITY TEST

The continuity function works best as quick and practical method to verify the existence of open circuit sections or short circuits. In order to obtain maximum accuracy when measuring resistance, use the resistance function (OHMS) of the meter.

### MEASUREMENT OF AC and CC tensions

With the function selector in the VDC or VAC position it makes a CC or AC voltage measurement based on the input applied between the V + y. This function also establishes the input impedance of the meter at approximately 3 kohms to reduce the possibility of erroneous readings due to parasitic voltages.

### MEASUREMENT OF AC AND CC MILLIVOLTS

With the function switch in the position of the multimeter measures millivolts of AC or CC.

### MEASUREMENT OF ALTERNATE AND CONTINOUS CURRENT

To avoid personal injury or damage to the meter: Never try to measure a current in a circuit when the voltage of the open circuit to ground is greater than 600 V. Before performing the test, check the meter´s fuse. Use the terminals, the position of the selector and the appropriate range for the measurements. Never place the probes in parallel with a circuit or component when the conductors are plugged into the current terminals A (Amps). Disconnect power from the circuit, open the circuit, insert the meter in series with the circuit and reconnect the power supply.

### MEASUREMENT OF CURRENTS GREATER THAN 10 AMPS

The millivolt and voltage function of the multimeter can be used with an optional output current probe to measure currents that exceed the nominal value of the multimeter. Make sure than the measurer has the correct function, AC or CC, selected for the current probe.

### MEASUREMENT OF FREQUENCY (SOME MODELS)

The meter measures the frequency of a signal by counting the number of times it crosses an activation level in every second. The activation level is 0 V, 0 A for all ranges. The frequency works only with the AC functions.

### DETECTION OF THE PRESENCE OF AC VOLTAGE (SOME MODELS)

To detect the presence of AC voltage, place the top of the meter near a conductor. When voltage is detected, the meter emits an acoustic and visual signal.

Erick Méndezmultimeter