The low pass filter also allows for accurate current measurements when used with Hall-effect type clamps. With the filter selected, the readings for both voltage and frequency (motor speed) should agree with the associated drive control display indications, if available. The incorporated selectable low pass filter allows troubleshooters to take accurate voltage, current, and frequency measurements on the output side of the drive at either the drive itself or the motor terminals. With the bandwidth and shielding issues combined, many True RMS meters display readings as much as 20 to 30% higher than what the drive controller is indicating. And if the DMM isn't shielded for high-frequency noise, the drive controller's high noise levels make the measurement discrepancies even more extreme. Many of today's True RMS digital multimeters have bandwidths out to 20 kHz or more, causing them to respond not only to the fundamental component, which is what the motor responds to but to all of the high-frequency components generated by the PWM drive. The causes of this discrepancy are bandwidth and shielding. A True RMS DMM reads the heating effect of the non-sinusoidal voltage applied to the motor, while the motor controller's output voltage reading only displays the RMS value of the fundamental component (typically from 30 Hz to 60 Hz). On the flip side, a regular True RMS multimeter can't reliably read the output side of a pulse width modulated (PWM) motor drive, because the ASD applies pulse width modulated nonsinusoidal voltage to the motor terminals. A significant unbalance may lead to erratic drive operation and should be corrected when discovered. The input voltage readings should be within 1% of one another when measured from phase to phase with no load. Drive measurementsĪny good quality True RMS multimeter can verify proper input power to an ASD. Now, technicians won't have to guess whether the drive is operating correctly and delivering the correct voltage, current, or frequency for a given control setting. Incorporates a selectable low pass filter* that allows for accurate drive output measurements that agree with the motor drive controller display indicator. But until now, there hasn't been a digital multimeter on the market able to accurately measure ASDs. This is especially true when taking voltage, frequency, and current measurements on the output side of the motor drive. Likewise, choosing the right test tools for troubleshooting the drive, the motor, and the connections are of utmost importance. Nobody takes inaccurate measurements on purpose, but it's easy to do, especially when working in a high-energy, noisy environment like an ASD. As you go, take care to take accurate measurements. A lot of time and money can be wasted replacing perfectly good parts when the problem is simply a loose connection. The most efficient troubleshooting procedure begins at the motor and then works systematically back to the electrical source, looking for the most obvious problems first. The trick is tracking it down quickly and keeping downtime to a minimum. Technicians use many different methods to troubleshoot an electrical circuit, and a good troubleshooter will always find the problem - eventually. Min/max/average with elapsed time to record signal fluctuationsīeeper on 250 detects opens or shorts of 500 µs or longerĬlick here for complete specifications on the Fluke 115.True RMS for accurate measurements on non-linear loads.Compatible with optional magnetic hanger (ToolPak™).Compact ergonomic design for one-handed operation.Large white LED backlight to work in poorly lit areas.Measures 10 A (20 A overload for 30 seconds).Measures resistance, continuity, frequency, capacitance, and diode test.Additionally, this digital multimeter is independently tested for safe use in CAT III 600V environments. This tool measures the True RMS voltage as well as currents with 6000 count, resistance, continuity, frequency, and capacitance for quick verifications. Ideal for general purpose electrical and electronic test requirements, this True RMS digital multimeter also provides simple, one-handed operation and compact design for field service technicians. The compact, general purpose troubleshooting tool for field service technicians
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