Testing

Testing

In this section we are going to cover:

  1. Introduction to The Multimeter
  2. Measuring voltage
  3. Measuring resistance
  4. Measuring current
  5. The Clamp Meter
  6. Auto-Ranging
  7. Interactive element

1.0 The Multimeter

A multimeter allows us to measure Voltage, current, and resistance, but it's important that we set the multimeter to the correct settings and and use the correct lead connection points for the task in hand. Watch the lesson below to see how we measure Voltage and resistance with a standard multimeter.

Please note video lesson below may take a while to load up...


2 Measuring Voltage

How to use a Multimeter (Voltage DC V & mV)

In the video above we covered how to set up a standard multimeter for 2 very different voltage tests:

  • 20V DC Testing in parallel (between the positive and negative terminals). Such as a 12v Battery Positive and Negative, or a 12v load such as a lamp. We selected a range close to and above that to which we need to measure, however, many meters are auto ranging, so you are only required to select the DC volts setting.
  • 2000mV DC Testing over terminals. Such as finding faulty connections between a battery post and the battery clamp. We are expecting voltages less than 20mV for a good connection. We chose a range close to and above that to which we need to measure, however some meters are auto ranging so you just select mV.

3 Measuring Resistance

How to use a Multimeter (Resistance Ohms Ω)

The multimeter is great for measuring resistance, and this is very useful for testing engine sensors, as we saw in the lesson above. Sensor manufacturers publish tables of resistances corresponding to the various values the sensor is required to measure, this can be confirmed by measuring the resistance of the terminals of the sensor / sender unit. When measuring resistance the meter runs a small current through the device to see how well it conducts, so the device must be disconnected from the circuit to be tested.


4 Measuring Current

How to use a standard Multimeter (Current Amps A)

When measuring currents with a standard multimeter, up to 10A, we have to interrupt the circuit and measure in series, with the positive test lead placed in the AMPS socket, and the black as always in the COM socket. The full circuit current actually flows through the meter. The big problem with this is we can only measure up to 10 A and if more current flows it can damage the meter, or blow an internal fuse, preventing any further current measurements. So for this reason I do not recommend measuring current with a standard DC multimeter, it's much easier and safer to use a DC Clamp meter, see below...


5 The DC Clamp Meter.

The DC clamp meter can measure voltage and resistance just like a standard multimeter, but it can also measure DC and AC currents without the need to interrupt the circuit.

How to use a Clamp Meter (Current Amps A)

I strongly recommend investing in a DC clamp meter as this will allow you to measure currents up to 200A without the need to interrupt, or make any electrical connection, it simply clamps around an individual conductor and measures the magnetic field to deduce current.

Please note video lesson below may take a while to load up...

The clamp meter measures the magnetic field around the cable and uses this value to calculate the current.

This device can be used to:

  • Check for parasitic loads on your batteries; when everything should be off.
  • Measuring alternator performance.
  • Diagnosing starting issues
  • Measuring the consumption of a particular device
  • Measuring the consumption of an entire circuit

Throughout this course you'll learn how to put this knowledge to good use for general testing, maintenance, fault prevention, and fault finding.

6 Auto Ranging

The multimeter below is an interactive element, so you can click any of the symbols around the dial for a description, and observe where the leads should be inserted. The type shown is what's called 'auto ranging' so you do not have to keep selecting the range of values you intend to measure, although there are separate settings for measuring very low values such as millivolts (mV) and milliamps (mA)

Remember - measuring current with a multimeter such as the one below requires that you actually run the current of the circuit being measured through the meter so it is critical that the leads are connected properly, and any current (AMPS) measured does not exceed the maximum rating of the meter. Most good quality multimeters have a replaceable fuse inside the meter, whereas the cheaper ones do not and can be permanently damaged by over current.

Tip: Use a DC clamp meter to measure current rather than a standard multimeter.

Tip: Check the condition of the meter, and leads before measuring higher voltages.

7 Interactive element

Click on the different symbols of the multimeter below to help you learn:

1) Correct lead placement, the meters leads must be in the appropriate sockets for the function you have selected

2) The names of the various functions, and how they can be used.

Click on the symbols around the dial to get started.