## The 3 Types of Digital Readouts

When using an analog scale, a pointer swings to the correct characters/digits that are physically on the scale in different locations. Digital readouts, however, must include multiple digits in one location. To see how this is accomplished, we are looking at three different digital display methods: dot matrix, solid character, and bar segments.

## Methods For Measuring Currents

Last week, we published a blog post going over the tools and methods used to measure electrical voltage in various situations. This week, we are taking a look at tests for measuring electrical currents- an essential step in electronic equipment maintenance that can identify the root cause of any failures and malfunctions. We will look at how to use ammeters, the importance of wire size, and how to test currents in power lines, heater motors, and air conditioners.

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## Methods For Testing Voltages

Measurements of electrical voltage are used to determine the possible differences in electric charge between two different points in an electric circuit. This data makes it possible to ascertain how much power is being used by a specific object, compared to how much power is available in the circuit. Since it allows us to ensure that an electrical circuit is operating both correctly and safely, this information is essential for the design, installation, and operation of electrical systems.

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## Identifying Harmonic Distortion

Ever since the first generators, harmonics have been a part of power systems. However, we now live in an era of power that is defined by non-linear loads. Equipment for powering computers, electronic ballasts, and VFDs are among the electronic power supplies that are used now more than ever. Unchecked harmonic distortion in these electrical equipment systems can result in damage and hazards such as overheating. Not only does this affect power quality, but it can become costly to fix. The question then becomes: do you know how to correctly measure the waveforms of your equipment while taking harmonic distortion into account?

## Calibrating and Measuring Accuracy in Analog Meters

All electromagnetic current meters function on the basis that the intensity of the magnetic field around a coil is proportional to the amount of current flowing through it. Whether the meter you are using is alternating current (AC) or direct current (DC), knowing what to expect from the different meter movements is essential for correct calibration and accurate measurements.

## Ohmmeters: Measuring Resistance

Multimeters are current meters, voltmeters, and ohmmeters contained in one case. There are separate current, voltage, and resistance circuits interconnected by switches and they share the same meter movement. A function switch is utilized to choose the type of measurement: position 1 is for de volts and resistance, position 2 is for de and ac current, and position 3 is for ac voltage. The jack on the right, the COMMON jack, is used for all measurements. For every type of measurement, the range switch is set for the correct scale reading. Positions I and 2 are resistance ranges, positions 3 to 6 are current shunt settings, and positions 7 to 9 are voltage multiplier settings. Rectifiers D1 and  D3 are linked for ac current measurements and rectifiers D2  and D3 are used for ac voltage measurements. Fuse FI safeguards the meter movement from overload. Resistors R1, R2, R7, R8, and R9 are switched in and out of the circuit by the range switch. The current shunts, R3 to R6 are only linked into the circuit in position 2 of the function switch. The range switch then chooses portions of the ring shunt.

## How To: Reading a Meter Scale

Whether you install, operate, repair, or design electrical equipment, you must know how to measure and test many types of electrical characteristics. The most imperative of these are electrical current, voltage, and resistance. Additionally, there are various applications that also require the testing and measuring of power, power factor, frequency, impedance, and sensitivity, as well as special component characteristics, such as capacitance and inductance.

# Checking Wattmeter Power Loss

The stationary (current) coils and the moving (voltage) coil of a wattmeter have resistance, resulting in some circuit power loss by the wattmeter.  Unless this power loss is considered, incorrect power readings will result.

## Power Meters

Calculating Power

If you wish to find power dissipated in an electrical load, measure any two of the three basic electrical quantities- current, voltage, and resistance. For example, you will recall that power can be calculated by multiplying voltage by current: P = VI. Therefore, if you use a voltmeter to measure the voltage across a load, and a current meter to measure the current flowing through the load, insert these values into the power equation. Similarly, you can measure current through the load and the resistance of the load, and then calculate power with: P = 12 R. Or you can measure the voltage across the load and use the equation: p = y2; R.

## Digital Meters

Input circuits allow the input voltage to be stepped down by the ranging circuits, which could be a switch or automatic circuits. The ranging circuits also select the proper pulse stream from the clock and divider circuits. The test voltage is amplified and integrated with the gate pulse to produce a ramp voltage that will pass a selected sample of pulses. The number of pulses passed is related to the test voltage. These are shaped and counted, and then decoded to drive the seven-segment displays.