Logic Probe vs Multimeter: What are the Differences?

Logic probes and multimeters are both essential instruments for technicians. These are measuring devices used to measure specific quantities that help technicians or engineers quickly troubleshoot machinery. But when it comes to using both instruments, some tech workers get confused. That's what we're here with a detailed comparison between logic probe vs multimeter.

What is a Logic Probe?

A logic probe is a low-cost probe containing a pen-like tube and three indicator lights to display the state of a line being probed. It allows you to keep a glance at signals of an operating circuit according to the requirement. 

In a logical probe, technicians do not have to connect wires to LED or signal monitors. The logic probe is usually powered by the circuit, which is tested through alligator clips attached to the under-test circuit and ground.

What is a Multimeter?

A Multimeter is a digital device used to test multiple electric values in a circuit, including electric current, resistance, and voltages. Multimeters are standard analog diagnostic tools used by technicians and electricians for troubleshooting problems in all types of electric appliances, power circuits, motors, and HVACs.

When comparing logic probes and multimeters, multimeters are more advanced, having many extra features according to the requirements of the tests in different kinds of electric circuits.

Check out this recent article explaining how to use and safely read a multimeter.

Appearance Comparison Between Logic Probe and Multimeter

The Appearance of a Logic Probe

Logic probe circuits are found very simple and easy to understand. However, there are different kinds of logic probes available. They are only slightly different from each other and are the same in basic functionality. Before using any type of logical probes, you must know and understand the connections. 

Two leads are coming out from opposite ends of the device onto the probe on a logical probe. Red lead is connected to the probe, and the black lead is connected to the ground, which is used as a return. 

Red lead can be totally red or have some red somewhere on it, and possibly it can be red only from alligator clips used to connect logical probes to the circuit.  

 Most advanced logical probe circuits have three LEDs in the body of the circuit. 

1. An LED to mark a high logic state (1)
2. An LED to mark a low logic state (0)
3. An LED to show fluctuations in low and high states. A pulse detector is connected to a third LED, which helps display even short pulses on the LED.

The circuit of the logical probe requires a supply of power equal to the power supply of the circuit of the device you are going to test with the logical probe. This is because logical probes depend upon the supply of the device it is testing.   

Technicians should connect the logical probe with the circuit carefully as it is an open and delicate circuit. If it falls on the device, it can cause a short circuit in the device and even in the probe itself, damaging both the probe and the device it is testing.

The Appearance of a Multimeter 

While comparing digital probes and multimeters, the multimeters are more compact in structure and easy to use.

A multimeter is basically a union of an AC meter, a DC voltmeter, an Ohmmeter, and an ammeter.

A multimeter contains an LCD and a knob to choose the three electrical values you want to measure. The multimeter consists of a circuit present inside the outer safety box with a coordinator circuit and an analog converter to convert 1 and 0 into the digits. This is why it is called a digital multimeter.

A printed circuit board (PCB) is present inside, consisting of concentric rings that connect and disconnect to the circuit according to the position of the knob.

When you select the required rand and parameters, the related part of PCB gets activated and performs the relevant functions and measurements. 

When you need to measure the resistance from an unknown resistor, the voltages get amplified over the resistor and pushed analog to digital converter, converting input resistance into digital values and displaying it on the digital display screen. 

When you measure an AC voltage, it should be first un-attenuated to acquire the suitable range, and after that, it is rectified to the DC signal. Then the analog signal converts the feed into a digital number and displays it on the screen.

Logic Probe vs Multimeter – Measurements

Measurement of a Logic Probe

As the logic probe is very basic in structure and function and can measure limited values.

• Logic high state probes are used to test circuits that are at high logical and digital states. Logic probe displays this with an LED that is commonly colored red.
• Logical low-state probes are used to test circuits that are logically and digitally at a low state. Logic probe displays this with an LED that is commonly colored green.
• Digital pulses can be detected by logical probes, which are incorporated into the circuitry for pulse detection. When this line is activated, the LED shows a third color, possibly amber. Some probes may be well designed to detect even short pulses. The brightness of the LED can estimate the length of the pulses.
• Line tri-stated detects a line on the probe when the connected device has its power output to the logic circuit turned off.

Measurement of a Multimeter

As compared to digital probe, the multimeters can measure a vast number of electric values, including:

• DC voltage and Amperage 
• DC voltage and Amperage 
• Frequency in Hz 
• Inductance henry
• Duty cycles 
• The temperature in Fahrenheit and Celsius
• Capacity in Farads 
• Resistance in ohms 
• Decibels

Some more advanced multimeters can also detect alkalinity, wind speed, acidity, light intensity, and humidity.

Safety Precautions to Use Multimeters & Logic Probes

• Before taking measurements, it is necessary to inspect the instruments for any physical damage visually.
• Make sure the plugs are tightly placed where there is no rust or extra dust present. 
• The wooden case of the logic probe and the outré safety box of the multimeter should be intact. Do not use damaged or cracked devices. 
• Read the user manual of every logic probe or multimeter carefully before using it.

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