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Diagnostic Tools Used for Generator Testing

Electrical/Electronic Diagnostics

Common Electronic Test Meters
Advanced power generators are a complete integrated system. The engine operating software can be controlled by commands from a system controller, such as a Cummins PCC controller. Technicians use a variety of electrical/electronic diagnostic tools to test and troubleshoot power generation systems. 

Multimeters, megohmmeters and clamp-on ammeters are some of the hand-held diagnostic tools needed. Portable load bank testers supply an external load to accurately test the generator under a controlled load. Manufacturer software is installed on service tools (laptop computers) to communicate with generator control systems. 

This article provides information on the function and common uses of both hand-held devices and software diagnostic tools. Generator Source always suggests using a trained power generator technician, licensed commercial electrician, or electrical contractor when working with any electrical equipment.

Hand-Held Meters


Multimeters are one of the most common tools our power generation technicians use on a daily basis. These meters are used to check for opens, shorts, and grounds in a circuit and more. Resistance, voltage, and amperage selections are common. Early multimeters were analog, and a needle moved across a scale. Today's multimeters are a digital multifunction electronic test tool with many capabilities.

Voltage tests are competed without isolating the circuit. However, amperage tests are a bit more complicated because the circuit must be routed through the multimeter. Conductors and coils are disconnected from the circuit when taking resistance readings. Generator stator winding specifications dictate the resistance of an individual coil. If the coil resistance is above specification, the alternator must be replaced or reconditioned. The resistance between individual coils must be infinite (OL).

The multimeter is the go-to meter for field technicians. It is the most reached-for tool in a technicians arsenal.

There are many adapters available to increase the meter capability. Below are some examples:
  • Clamp-on Current Transformer - Equips standard multimeter with clamp meter capability
  • Inductive Pick-Up/External Trigger - Allows technician to measure Revolution Per Minute (RPM)
  • Pressure Vacuum Module - Adds digital vacuum and pressure readings to multimeter
  • Integrated Temperature Probe - Allows multimeter to measure temperatures
There are many additional accessories for multimeters. For more information on one of the most popular manufacturers of Multimeters, visit the FLUKE website.  

Clamp-On Ammeter

Clamp Meter Circuit Test
Alternating Current (AC) clamp-ammeters have two ferrite or soft iron jaws wound with wire. The jaws are opened and closed around the conductor. When electrical current flows through a conductor, a magnetic field is produced. The magnetic field fluctuates proportionally to the load. A current transformer inside the meter translates the field fluctuations into an AC amperage reading. 

Direct Current (DC) clamp-ammeters are constructed with hall effect sensors. DC current flows in a fixed polarity and the magnetic field around the conductor does not change. The jaws are clamped around a conductor. The fixed-polarity flow produces a small amount of voltage. The ammeter hall effect sensors translate the voltage to a DC amperage reading. 

The cause of a circuit breaker trip can be a lengthy and difficult issue to solve. After short circuit issues have been eliminated, the ammeter allows the technician the ability to quickly determine if it is a failed circuit breaker or circuit overload condition. For more information on Clamp Meters go to the AMPROBE website


These are sometimes referred to as megger testing and advertised as an insulation tester. Heat is generated as electricity flows through a wire or coil. Insulation can break down due to excessive heat or time. The megohmmeter passes high voltage low amperage through a wire or coil. A common rule of thumb is insulation is acceptable with anything over 1 mega ohm reading. Alternators must be replaced with degraded or damaged stator winding insulation. Any wire in a control system that has heat damage to insulation should be checked and replaced. For more information on insulation testers like one of the ones shown to the right,  visit this Amprobe Resistance Tester page.

MegohmmeterDigitally Controlled Systems

A power generation system (such as a diesel generator) can be broken into the three main components:
  • Prime Mover - Engine and associated support systems.
  • Alternator - Produces electricity. Also referred to as a Generator End. Frequency is determined by rotation speed. Output voltage by stator configuration.
  • Control System - Interfaces engine with alternator to accommodate load demand.
The control system is constructed in a Programmable Logic Control (PLC) configuration. A power supply converts input panel supply AC and converts to DC for Central Processing Unit (CPU) use. The CPU receives inputs and transmits outputs via the I/O portion. The input and output are low voltage DC signals. These signals can take place so quickly that conventional hand-held meters cannot measure the transition. 

The CPU receives inputs from the system, calculates the proper outputs, and distributes appropriate component. Inputs are received from components like; temperature sensors, speed sensors and pressure sensors. Outputs are sent components such as; Light Emitting Diodes (LED), injector fire signals and internal system relays. 

It is close to impossible to troubleshoot, repair, test and monitor these advanced systems with just standard hand-held meters. The control panel indicates errors and operating condition abnormalities. Some of them feature condensed troubleshooting steps. Many manufacturers offer an electronic service tool as an option. Technicians can access the controller for testing, history and detailed operating parameters. For Cummins PCC information, go to Generator Set Controls Accessories

Both electronic service tool and hand-held meters are often used in troubleshooting complicated systems. An example of this is below:

The generator shuts down during normal operation. The technician accesses the controller and three out of five injectors have alarm conditions. Open circuit alarm and short circuit alarms are both present. Software cannot locate exact cause. Output from CPU is disconnected and resistance tests support alarms. Injector harness inspection reveals melted harness because of failed harness hanger. Injector harness is replaced, and unit is tested. 

Our technicians are well versed in the use of troubleshooting procedures and electronic tool usage. Contact Us with any generator service needs or questions.




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