When designing electric motors, special consideration is given to generating balanced loads, i.e. the neutral does not carry current. If the star is not led out (no neutral and thus three-wire circuit), an "external virtual star" can be configured. The G068-2 adapter provided by HBM can be used for this purpose. The G068-2 comprises three RC networks. The box precisely fits onto the MX403B's banana sockets, however, it limits the range to AC 600 V.
Electric current can be measured based on different principles. While a zero flux converter, shunt or Hall sensor converter allow for precise, phase-synchronous measurements of small currents, current probes are particularly suitable for quick current measurements in 1-phase and 3-phase operation. Current clamps enable a wide range of electrically isolated measurements of alternating currents (often also direct currents) without the current carrying line having to be opened. Furthermore, current clamps are inexpensive and allow for power analysis in applications with less stringent accuracy requirements. Different designs of current probes are available for different purposes (inductive, Hall effect).
The inductive measurement principle results in a phase delay in the current transformer (skewing) between the current clamp's real current and its output voltage, which needs to be compensated for prior to calculating the power. This involves correspondingly delaying the measured voltage. With some current clamps, the phase angle error varies according to the frequency and over the measuring range, which, of course, impacts on the power calculation! Depending on the measuring range, 3 to 10° can occur at reference conditions. Please note: a perfect sinusoidal voltage, 45…60 Hz, 23° C ambient temperature and 50% relative humidity are used as reference in most cases. Every deviation from this reference can and will impact on the accuracy of the current measurement and thus of the power calculation. Therefore, selecting the right current clamp is of paramount importance. For this reason, HBM directly offers current clamps.
The phase shift needs to be compensated for to enable the power calculation to be performed correctly. The easiest way to compensate for the phase shift and thus determine power is to delay the measured voltage correspondingly. This process is described in more detail below. Now that both electrical quantities have been discussed, we can consider the software required for calculating electrical power.
Data acquisition - fast, safe, reliable: Data acquisition systems and measuring amplifiers need to meet stringent requirements today. Read our numerous technical articles on the topic to learn which rules need to be complied with and which data acquisition trends we will have to expect in the future.
HBM catman DAQ software is ideally suited for measurement acquisitions in the following steps in your calculation:
In addition to measurement acquisition, catman software also offers an integrated mathematics library. The mathematical functions include simple algebraic calculations, statistical and spectral analyses, and calculation of electrical power and efficiency. The software can also calculate root-mean-squared (RMS) value of input quantities.
A sensor database can help you to parameterize the measurement channels. If the correct signal description cannot be found in the sensor database, you can check the relevant data sheet. Using the sensor data sheet makes it easier to set the parameters of each individual channel later and it makes the process reproducible at any time.
Due to their inductive measuring core, current probes have a phase delay. This means the phase of the converter's output signal is delayed relative to the current phase. If the phase delay of the converter is not known, it can easily be gaged by measuring the current and voltage on a resistive consumer (for example, a filament bulb) and correcting it using catman EASY software. The measured voltage can be delayed correspondingly. For example, current probes can be connected to the QuantumX MX403B module using a banana-to-Bayonet-Neill-Concelman (BNC) adapter.
The current probe can also be connected via another measuring amplifier in a group such as a BNC-to-SubHD adapter on the MX840A universal amplifier. This amplifier is also able to record the following variables: torque, rotational speed, temperature, acceleration, vibration and CAN bus signals.
On the right side is an example of the phase correction in catman: Computing channels > Filter > Phase correction function
Power calculation considers low-frequency harmonic signals only (< 100 Hz). The process does not involve any complex integration algorithms. Common standard formulas are used. Power calculation in catman Easy incorporates a window-based process. The accuracy of the power calculation thus depends on the fundamental frequency of the signal and the width selected for the window. The calculated power will exhibit a slight residual ripple, even in a static system.
For example: 50 Hz fundamental oscillation -> 20 ms per period -> 100 ms window -> 5 periods on average.
Complete calculation of all quantities in catman EASY includes the RMS value and also the mean value (MEAN) over a time window. Neither one is formed in a straight forward averaging process with n values, as in the QuantumX MX403B module, as an example. (This would require a buffer for n values, so maximum time window would be limited!) Instead, the process is a one-step iteration with no buffer. The formulas are as follows:
The process is faster, requires practically no buffer, and can therefore implement time windows of any size. The result agrees closely with the values calculated on-board a QuantumX MX410B or QuantumX MX403B amplifier. RMS and MEAN can also be filtered for smoothing. The other computing channels are calculated as follows:
Subsequently, a signal analysis in the frequency range is performed. A signal analysis of this type is based on the Fast Fourier Transform (FFT). It facilitates the transition from time signals to the frequency range. Using catmanEasy measurement software, you can visualize and analyze the frequency distribution of one or multiple signals. Below, the number of measured values used for calculating the amplitude spectrum is a required parameter.
Frequency analysis in the post-process mode uses the FFT to calculate a spectrum (an amplitude, phase or power spectrum). Displaying multiple spectra over time is especially important in dynamic operation. A "waterfall diagram" can successively display amplitude spectra tiered in three dimensions. The view can be freely rotated in all directions. Activate 'Generate Frequency Data Set' to have the frequency channel available for export.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
