Digital MultimeterPublished on 24/2/2012 & updated on 31/7/2018
Parts of Digital MultimeterA multimeter is a simple but useful device which has only three parts; Display screen, selection knob, ports.
Display screen-It has illuminated display screen for better visualization. It has five digits display screen; one represent sign value and the other four are for number representation.
Selection knob- As we know a single multimeter performs so many tasks like reading voltage, resistance, and current. The selection knob allows the user to select the different job.
Port- There are two ports on the front of the unit. One is the mAVΩ port which allows the measurement of all the three units: current up to 200 mA, voltage, and resistance. The red probe is plugged into this port. The other is COM port which means common and it normally connected to –ev of a circuit and black probe is plugged into it. There is one particular port is 10A, which is use to measures large current in the circuit.
Features of Digital MultimeterNow a day, wide range of digital multimeters are available in the market. But their features make it a good multimeter. Some of the features which are very useful and should be there in a multimeter are:
Auto-Rang This feature enables multimeter to change their internal range according to the requirement to detect the correct voltage, current, or resistance of the circuit. It has an ability to stop the meter at the particular range and prevent the overloading if the meter is in volt range. Such multimeters are of high quality and have more features.
A Back-Lit LCD It is a fancy feature, but felt very useful in dark situations when there is no other light source for watching reading in the multimeter.
Auto-Off It is a great feature but normally comes in higher end version. It facilitates user to forget to turn the meter off when it is not in use.
Decent Probes Decent probes are bonus above all. In multimeters normally leads are used which get damage at flex point. So it is better to use probes which make work easier and easy to replace if get damaged.
Auto Polarity It is an important feature that shows the polarity of the current. When the voltage of current being measured shows positive reading (i.e. same polarity to meter connections) and if it shows negative (i.e. opposite polarity to meter connections). Such facility was not available in an analog multimeter and the meter deflects backward and reverses back to take the reading accurately.
Tutorial for Current MeasurementThe measurements of voltage and resistance are most simple and can be done with certain precaution if required. But in the case of current measurement firm precaution is obligatory. Reading current is quite tricky because current should be measured in series. To do so, the flow of current is interrupted and keeps the digital multimeter in-line so that current passes through DMM. The rest of the connection is same as done in the case of voltage measurement and resistance. Digital multimeter has two ports; A and µA mA for measurement of current. The reason behind the two ports is to avoid overloading. In digital multimeter current has to pass through a fuse and if large current passes through the fuse it will blow out. A port is designated for large current and µA mA for small current. For measuring large current, plug one of the cords in A port and other in COM port. For measuring small current in a circuit, plug one cord in µA mA and the other in COM. While doing the connection, one more thing keeps in consideration and that is the direction of the current. A multimeter is connected in such a way that current enters from A port and leaves the DMM from the COM port, as shown in a figure. Most of the multimeter uses direct current. But if the circuit is drawing alternate current then you should use non-contact tester rather than the multimeter.
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