Digital Multi-Meters: A very handy tool for Electrical Engineers

An electrical engineer and electrician must be familiar with a variety of test and measurement instruments. They need to know how to use these instruments in a safe and proper way under different working conditions. It is important to use the right tools and instruments when working with electricity. Appropriate equipments can make a hard task easy and at the same time wrong selection can make an easy job difficult and dangerous.

This article looks at the most common type of meter available with an electrical engineer or electrician; i.e. the Multi-meter. 

Another versatile and handy instrument for an electrical engineer, particularly in the Solar PV field, is the digital clamp meter. 

Multi-meters are hand-held instruments designed to measure more than one electrical value; for example DC and AC voltages, DC and AC current, resistance etc. They are also used to check the continuity of conductors or to check the diode. Figure 1 shows the icon of some of the electrical quantities measured by a multi-meter.

Fig.1: Icon of some of the electrical quantities measured by a multi-meter.

In other words, a multi-meter is a measuring instrument that combines an ammeter, a voltmeter and an ohmmeter to measure the current, voltage and resistance in a circuit; means no need to carry different meters for measuring different values.

Digital Multi-meter:

Both analog and digital multi-meters are available, but the digital version has superseded the analog one. Digital Multi-meters (DMM) has a digital display to show the measured values, a dial or selector switch to change the mode of the meter, and connecting terminals. Figure 2 shows a low cost commonly available DMM.

Fig. 2: Low cost commonly available DMM.

Accessories such as a pair of red and black probes, is also provided with the meters. The black probe is always considered as the negative probe and is connected to the common terminal. Figure 3 shows the probe provided with the DMM.

Fig. 3: Probe provided with the DMM.

System with Harmonics:

When harmonics is present in the system, only true RMS meters can provide accurate measurement   of AC values. Harmonics are frequencies that are multiples of the fundamental frequency (50 Hz in India) and can cause distortion of basic AC waveform. The common loads which causes harmonics in the system are computers, fluorescent luminaires with electronic ballast, inverters etc. These electrical loads are also called Non-linear loads as their impedance are not constant.

Working of Digital Multi-Meter:

The basic circuit of a Digital Multi-Meter is always a DC voltmeter. The AC quantity is rectified into DC with the help of rectifiers and filters. All the quantities are digitised using an Analog to Digital Converter (ADC) and displayed in the digital form on the display.

Figure 4 shows the internal circuit of a commonly available Digital Multi-Meter.

Fig.4: Internal circuit of a commonly available Digital Multi-Meter.

Advantages of Digital Multi-Meter:

Digital Multi-Meters have the following advantages over analog:

1.       Cheap and compact,

2.       Accuracy is very high,

3.       No loading effect,

4.       Reading of values is much easier,

5.       Can be interfaced with external equipment,

Safety:

“Always read and follow the manufacturer’s instructions that are supplied with the Multi-meter. Equipments may be damaged badly and or the user may be seriously injured if proper safety procedures and instructions are not followed.”

Safety is very important when using test and measurement instruments. Many a times, the meter is used to make the measurement while the electrical circuit is energized. Ensure to follow the regular and standard safety procedures when working on live circuits. A safe working practice is always mandatory. The following safety tips are recommended-

1.       Ensure the correct position of selector switch,

2.       Do not be alone when working on live circuits,

3.       Keep your hands dry when taking measurements,

4.  Use rubber gloves and wear shoes when taking measurements on energized circuits.

Safety in Power Plants, Stations and Electrical Networks: A Collective responsibility?

Indian electrical power system consists of many generating stations, sub-stations, and transmission & distribution lines of voltage range 1200/ 765/ 400/ 220/ 132/ 66/ 33/ 11 kV. All the associated equipments of power system are monitored, attended, operated and maintained round the clock for un-interrupted and reliable flow of electricity throughout the country. New construction or capacity addition activities are also carried out simultaneously. Most of the operation and maintenance activities are done by regular engineers and technicians of the concerned organization, whereas bulk of the construction works is carried out through outsourcing.

The electrical and electronic equipments and systems used in any power system network are designed in such a way that they are safe during normal operation, but in case of mal-operation or faults they can be very dangerous.

This article is supposed to throw some light on safety aspects, and to grab the attention of our young engineers and technicians.

What is safety?

What the word safety means as far as electrical power stations and networks are concerned?

“Safety may be interpreted as proper planning of task, proper usage of safety tools and equipments, following safety procedures, exercising good judgement and intelligent supervision.”

Fig 1: A combination of unsafe working conditions,and unsafe activities.

 Analysis show that majority of accidents were preventable.

Safety: A Collective responsibility

With a massive growth and expansion of generating stations, substations, lines and associated systems, safety at work place is of prime importance. Accident do not “just happen”, but they are the outcome of unsafe working conditions, unsafe activities or a combination of both. 

Then who is responsible for the “safe working environment” in electrical plants and networks?

It is our, i.e. of electrical engineers, technicians, and contractors, collective responsibility to implement safety standards and maintain a safe working environment in the best possible way.

We must learn from past mistakes, evolve gradually and move towards an accident free atmosphere. The presently followed safety standards should be enhanced to minimize, if not possible to eliminate, accidents and injuries.

Rules, Act and Code to be followed:

One should follow the safety policy, statutory provisions pertaining to safety, responsibility assignment, hazard identification, and personnel protective equipments and tools.

All the electrical engineers/ technicians working on electrical power projects in India, must ensure compliance with the requirements of Indian Electricity (I.E.) Rule 1956, Indian Electricity Act 2003, Indian Electricity Grid Code and Central Electricity Authority (C.E.A.) Regulation 2010.

Role of Electrical Engineers:

As an electrical engineer it must be our policy to perform each task in the safest possible manner, together with good practice. The health, safety and well-being of our workers and all those who are likely to be affected, are our responsibility. Safety aspect should be kept at par with our business objectives. Not only the engineers, it is the duty of each worker engaged in power system construction, operation and maintenance activities to exercise due care and caution for his/ her own safety, of fellow workers, and the concerned equipment and system.

As an engineer, we must:

Ø  Provide safety information, instruction and training to the team,

Ø  Ensure that tasks are allocated to competent workers,

Ø  Ensure safe and proper handling and use of equipments,

Ø  Provide and maintain a safe plant and Equipment, and

Ø Consult with our fellow engineers, sub-ordinates, and technicians on matters affecting the safety.

Remember:

Prevention of accidents or mis-happenings requires a whole hearted co-operation of all the concerned. Usually it’s the capable and mentally alert worker who avoids the accident. Good luck.