Using multimeter VOM as Ammeter

The DC ammeter- is used to measure the direct current of a circuit. The unit of measure is ampere (A). An multimeter can be used as ammeter by connecting it in series with the circuit. It requires correct application and polarity to measure the current.

Procedure:
1. Check the pointer of the meter if it set to zero
2. Set the knob at DC and set it to the desired ampere range.There are different ranges including 250 mA ,25mA 2.5mA and 50uA .For safety, set the knob at the top level (250mA ) to gain rough value when the current range is unknown. If you can not read it conveniently try to lower the range of the meter gradually in accordance with the first rough data for precise measurement.
3. Connect the test leads in series with the circuit. Apply the pin of the red lead to positive and black one to negative.
4. Read the current value in the display

Note

• Do not touch the test probe.
• Observe the polarity of the meter if the pointer deflects backward or the value to be negative,remove the connection immediately and reverse the connection of the test probe.

How to use a multimeter as Ohmmeter

Ohmmeter- an ohmmeter  is used to measure resistance. Connected in parallel or across,  It can be used to check and measure the continuity of the circuit . When using  an ohmmeter it does not require correct application polarity.

Resistance test procedure:
    the purpose of the Ω test is to measure the resistance or checking out if the circuit is short or open . Here are the procedures in performing a resistance test using both analog and digital multimeter(DMM)

For Analog multi-meter

1. Set the knob to ohm (Ω).
2. Check the pointer of the multitester if it is set to infinite.
3. Set the multi-tester to the desired range. You can set the pointer initially at zero Ω by connecting the two leads of the instrument and adjusting the knob to be exactly zero.
4. Measure the resistance of  the component being measured. The reading is equivalent to the scale reading multiplied by the number indicated at the set range.  Ranges  are Ωx1, Ωx10 ,Ωx100, Ωx10k and Ωx1k 

         For Digital multimeter (DMM)
1. Turn off power and discharge all capacitors of the circuit  
2. Select "resistance" on the multimeter- You can switch to your designed ohm range position
3. Connect the test leads to the circuit to the device or circuit being measured
4  Read the resistance value on the digital display of the DMM

Note:

• Do not touch the pins (metal part) of the test lead t o avoid reading error caused by the resistance of the human body
• Don't make a resistance measurement while the circuit is with power. It may damage the meter by this improper operation
• for analog multimeter ,reset the pointer to zero  when changing the range of the ohmmeter.

Using a Multimeter/multi-tester: Preliminary setup and Safety precautions

Multi-tester (VOM-volt/ohmeter) also called multimeter is designed to measure different magnitudes of electrical units:voltage,current and resistance. It incorporates the functions of a voltmeter,ohmmeter,and Milli-ammeter into one device. A multimeter maybe Digital (DVOM/DMM) or Analog.

Parts and functions of multi-tester

Digital multimeter        Analog multimeter

1.   Zero ohm adjuster- for analog multi-testers this part sets the  indicator of the left scale to zero

2.   Range Selector switch knob-this is a switch that is calibrated to select the proper range of the meter

3. Amperage terminal -plug in connection for red (positive) test lead for measuring amperes 
4   +V.Ω.f terminal(positive )- terminal for positive test probe.It is  used for most types of measurements.

5.   -COM terminal (negative,N)- a terminal for the negative test probe

6.   Home plate-Serves as the cover or panel for multi-tester

7.   Indicator pointer- It deflects a certain point and use as a reference of where to read the measurement

8.  Output socket- used for measuring special purpose such as high AC  voltage,intensity of sounds in decibel,etc

9. Range Scale- it indicates the test function and scale option

10. Display for Digital multi meter(DMM) -it displays the measurement reading. Usually have a four digit display with a +/- indicator. 

Preliminary setup before measurement

1. Before start measuring, make sure that the pointer stays at zero(0) position on the left end of the scale. If not,gently adjust the zero corrector with the use of screwdriver to set it to zero.

2.Select the proper range before measuring. Do not attempt to switch the range knob while  measuring. Disconnect the test leads first before switching the range knob as it may damage your multimeter. in determining a measuring range,select a higher voltage than the value to be measured as well as where the pointer of the meter moves to considerable extent. however,select the maximum range and measure in case the extent of value to be measures can not be predicted.

Precautions for safety measurement

1. Never use meter on the electric circuit that exceeds 3k VA.

2. Pay special attention when measuring the voltage of AC30 volts or DC60V or more to avoid injury.

3. Never apply an input signals exceeding the maximum rating input value.

4. Never use meter for measuring the line connected with equipment that generates induced or surge voltage since it may exceed the maximum allowable voltage.

5.  Never use meter if the meter or test leads are damaged or broken.

6.  Never use encase meter.

7.  Be sure to use fuse of the specified rating type.never use substitute of the use or never make a short circuit of the fuse.

8. Always keep your fingers behind the finger guards on the probe when making measurements.

9. Be sure to disconnect the test pins from the circuit when changing the function of the range.

10. Before starting measurement,make sure that the function and range are properly set in accordance with the measurement.

11. Never use meter with wet hands or in damp environment.

12. Never open tester case except when replacing batteries or fuses. Do not attempt any alteration of original specifications.

13. Never use test leads other than the specified test leads.

14. To ensure safety and maintain accuracy,calibrate and check the meter at least once a year.