How to Test a Diode with an Analog Multimeter

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Troubleshooting in electrical engineering and electronics is a vital part, and you should understand the basic knowledge and skills about the components to design and troubleshoot a circuit. We recommend that you test the component first before you start assembling and putting it in a circuit. 

Often, you get shocking and odd results. That’s why it’s important to do tests first to determine whether the device and component are working correctly, or you should change it with a new one. In today’s post, we will talk about how you can test a diode with an analog multimeter. 

Testing a Diode 

A diode is a tiny device in an electrical circuit that enables an electric current to flow through a single route. It functions by having low resistance in one direction and high resistance in the other direction. 

You will have to test a diode—that is normally made from a semiconductor material—to ensure it is working accordingly. You can check the health of an average diode with either an analog or digital multimeter that will measure in volts or ohms. 

But for this article, we will focus on using an analog multimeter to test a diode. 

What is an Analog Multimeter? 

An analog multimeter works based on the refraction of a needle from its zero-position point. You need to read the right value under the needle during your measurement. 

The key part of an analog multimeter is a galvanometer which is composed of a small winding. The winding could rate about a pin, and a needle is connected to it. It’s worth mentioning as well that it features a spring to return the needle to the home (zero) position. It bounces from its rest position depending on the current’s intensity through the winding. 

Making some changes to a galvanometer and adding more components allows it to be used as an ohmmeter, voltmeter, ammeter, and other measurement devices. The needle’s refraction in an analog multimeter is always from left to right. 

What Can an Analog Multimeter Measures? 

Certain measurements made by analog multimeters include:

  • decibel measurement
  • frequency range of AC currents
  • AC current
  • DC current
  • DC voltage
  • AC voltage

Analog multimeters measuring current might have a current clamp built-in or designed as a probe. In case you didn’t know, a current clamp is a sensor, which surrounds the wire. 

When looking for analog multimeters, you need to consider the measurement range for whichever value is measured. This type of multimeter shows such values through a dial, normally a needle or moving pointer. 

Further, analog multimeters are commonly handheld or benchtops. The latter can also be portable by the use of wheels and handles. On the other hand, handheld multimeters are especially created to be used while holding, such as being operated with one hand. 

What are its Features?

Typical features for analog multimeters include:

  • battery test
  • diode test
  • range switch
  • mirrored scale
  • temperature compensated
  • overload protection
  • battery power

Devices with battery power could be operated with no plug-in power. Remember that multimeters having overload protection with a fuse or other method aims to safeguard the meter. Temperature-compensated devices have electrical or programming devices created to counteract known mistakes caused by temperature fluctuations.

A mirrored scale makes it simpler for you to read the device to a specific accuracy by allowing the operator to prevent parallax errors. A range switch is utilized to pick a suitable range of units to be measured. A device with a diode test has processes for testing diode operation. 

Ultimately, an analog multimeter with a battery test has ways for testing battery operation. 

How to Test for Diode Using an Analog Multimeter?

Is the diode test not accessible in your digital multimeter? Maybe you have to test the diode with an analog multimeter. Whatever the case, resistance mode (Ω) can be utilized to test the diode instead. 

Here are the steps you need to follow to test the diode with an analog multimeter. 

  1. Disconnect the diode from the circuit and ensure the power supply is removed from the circuit. Also, make sure there is no voltage across the diode that has to be tested. You also need to discharge all the capacitors by shorting the leads in the circuits, if there are any. 
  1. Set your analog multimeter on Resistance mode (Ω). You can do that by turning the rotary switch of your analog multimeter. For better readings, set the Ω range on 1k Ω for forward bias and 100k Ω for reverse bias.
  1. Attach the red test lead to the anode of the diode. The black test lead should be connected to the cathode of the diode. Always take note of the reading and measurement. 
  1. Reverse your test leads. For instance, the black test lead to anode and the red test lead to cathode. Remember the measurement and reading shown by your analog multimeter.

Does your multimeter give 1k Ω to 10 M Ω? Then it indicates the diode is in perfect condition. Often, the ideal value is under 1k Ω. For instance, the forward bias resistance must be low for a good diode.

Does your analog multimeter show OL in reverse biased? It also indicates the diode is working well. If the meter shows the same measurement and reading in both directions, it suggests the diode is bad and needs immediate replacement.

Suppose your device shows the same readings (high resistance or low resistance or OL in both directions), the diode is open and short, respectively. In short, the diode is short if the multimeter shows 0 Ω resistance in both forward and reverse bias. The diode is open and needs a replacement if the ohmmeter shows OL or very high resistance in both reverse and forward bias. 

Would you like to ensure your results are always accurate? It will help if you test and compare the result of good diodes first in Resistance Mode.

Final Thoughts

There you have it! Testing a diode with an analog multimeter does not need to be that challenging. Just follow the steps we highlighted above, and you are good to go.

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