Fluke 438-II mechanical metering functions

Motor torque

Calculates the amount of rotational force (displayed in lb.ft or Nm) developed by a motor and transmitted to a driven mechanical load. The motor torque is the single most critical variable that characterizes the instantaneous mechanical performance of rotating equipment driven by electric motors.

Motor speed

Provides the instantaneous motor shaft rotational speed. Combined with the motor torque, motor speed provides a snapshot of the mechanical performance of rotating equipment driven by electric motors.

Motor mechanical load

Measures the actual mechanical power (displayed in hp or kW) produced by motors and provides a direct link to overloading conditions without simply basing it on the motor current.

Motor efficiency

Shows the effectiveness of each motor within a machine, assembly line, plant, and/or facility in converting electric power to useful mechanical work. By properly aggregating the efficiencies of a population of motors the total (aggregate) efficiency can be estimated. Comparisons to expected motor efficiencies at observed operating conditions can help quantify the cost associated with motor energy inefficiency.

How it works

Using proprietary algorithms, the Fluke 438-II Power Quality and Motor Analyzer uses three phase current and voltage waveforms to calculate motor torque, speed, load and efficiency at a 1 second update rate. The motor air gap field, as observed via the voltage/current waveforms, provides the basis for the measurements. Mechanical sensors and intrusive no-load motor testing is not required, making it faster than ever to analyze overall electric motor performance.

Simply hookup the voltage measurement leads and flexible current probes to the service supplying the motor.

Input details of the motor from the rating plate including rated power, rated speed and motor type from either NEMA or IEC classifications.

Note: Measurement units can be set to local requirements hp/kW, lb ft/Nm etc.

3 Fluke Corporation Fluke 438-II Power Quality and Motor Analyzer Electrical motor analysis

The Fluke 438-II provides a complete breakdown of electrical parameters. Prior to beginning motor analysis, it's recommended to make base line power quality measurements to assess the state of harmonics and unbalance on the electrical service output as these two properties can have a serious negative impact, on motor performance.

When in Motor Analysis mode, results are summarized for electrical performance, mechanical performance and derating (according to NEMA recommendations).

The easy to understand four-level color severity scale indicates motor performance in relation to the recommended electrical parameter levels including rated power, power factor, unbalance and harmonics.

For mechanical power you can instantly view the mechanical output power along with motor torque and speed. The mechanical output power is instantly compared with electrical power to provide you with live efficiency measurements. With this feature you can easily measure machine performance during each operation cycle.

The NEMA derating screen is updated as the load and the electrical conditions change, and each new measurement is plotted on the tolerance graph as a "+". In this example we can see that motor is within tolerance but is close to the service factor. This indicates that there may be a need for power quality mitigation, motor maintenance or some other performance improving adjustment. By frequently performing these tests over time, known benchmarks and performance trends can be created, enabling informed maintenance investment decisions.

Using Fluke Thermal Imaging to Troubleshoot Motors & Drives

Infrared cameras, also called thermal imagers, are useful for troubleshooting motor problems as well as for monitoring motor condition for preventative maintenance in power generation, manufacturing and commercial plants. Thermal images of motors reveal their operating condition as indicated by surface temperature. Such condition monitoring is important as a way to avert many unexpected motor malfunctions in systems that are critical to manufacturing. The onset of motor failures can often be detected by a variety of techniques, including vibration, ultrasound and thermal imaging.

In this article, we cover why use thermal imaging and what to scan, as well as some notes on what to look for, including shaft misalignment.