A typical diagnostic tool for technicians in the electrical or electronic industry, multimeters as the name suggests can measure current, voltage, resistance and continuity. These are the basic measurements a simple multimeter can provide. As a technician gets more experience, complex multimeters giving more measurements are required. There are analog multimeters which have a moving pointer to indicate values, and a digital one with digital readings. Nowadays Digital Multimeters or DMMs are used more than analog ones.
Use of multimeters:
Multimeters are used to test circuits while debugging as well as batteries. Usually the range has to be set before getting the actual measurements. Based on the expected value, this range can be manually set or it has auto range capabilities. A range of a twenty microamps through milliamps to 10 amps max, 200 micro Volts to 600 volts, and 200 ohms through kilo ohms to 20 mega ohms.. these are the ranges normally. It can be used for alternating and direct current by turning the knob appropriately. Auto range multimeters display the unit for the reading.
A multimeter shows average current. Capacitors and Inductors have an initial surge of current that cannot be detected by a multimeter and would require an oscilloscope to detect and measure it.
Continuity tests on diodes are to detect their polarity. Diodes (and resistors) have to be separated from any power source before measurements are done on them. In a circuit the continuity of diodes is indicated by a beep.
Applications of multimeters
Ham radio applications
Categories of multimeters
There are four categories based on their applications running from low risk – CAT I to high risk CAT IV.
Each category rating specifies the safe passing voltages for the measuring ranges in the multimeter. Category rated meters have inbuilt protection from current overruns.
Some advanced features of multimeters:
· Capacitance reading
· Frequency reading
· With a thermocouple probe, temperature readings are possible
· Storage capabilities of readings and transferring them through USB
· A multimeter is kept handy by every technician as it is the first diagnostic tool at hand for debugging circuit designs in electronics.
· Ability to interface with computers
What to look for when buying a multimeter:
These are the conditions that should be satisfied when choosing a multimeter:
· Safety features- they should be CAT rated and have a built in fuse for high currents.
· Voltage range and veracity of readings – depends on what you are buying it for. If it is for home circuitry, the measurements need not be too accurate, like you would be requiring for electronic circuits. You would need AC and DC measuring capabilities in most cases.
· Durability and the size – it should be of a good make to withstand a few falls now and then. A convenient size which fits into the pocket is preferred by many technicians, but for an irregular user, a large size could be more helpful, with easily readable values.
· Accessories – probes with banana plugs, needle tip probes, alligator clips, tweezer probes and a temperature probe which is useful in HVAC applications.
· Warranty – Some manufacturers give a lifetime warranty, the term lifetime being defined differently by each! Others give one year warranty. A lifetime warranty is always better, whatever the term might indicate, it would be better than a one year warranty
· Price – do not compromise on the price if that is a sticky factor, all other features among models being the same. This is a question of safety so if all the safety features are in place, don’t hesitate to spend a bit more.