The new models with True RMS are literally a precise supplement to the pioneering P 40000 high-voltage isolator series.
Whether working voltages up to 3600V AC/DC or test voltages up to 15kV AC, whether calibrated range selection or VariPower broad-range power supply, whether extreme performance or compact modular housing – Knick has transferred this ideal combination of product properties of the VariTrans P 40000 to the measurement of AC signals, thus defining a completely new class of AC/DC transmitters.
The AC/DC high-voltage transmitters transform the RMS value of the alternating input voltage or current into a standardised direct current or direct voltage signal. The output signal is safely galvanically isolated from the input signal and the voltage supply.
RMS or rather TRMS
Simple AC/DC transmitters operate according to an averaging technique, which uses the form factor for sinusoidal waveforms (RMS value / arithmetic mean = 1.11) to transform RMS values.
Here, the RMS (root-mean-square) value is the effective value of a sinusoidal AC signal. A measurement technique using the correction factor 1.11 is only suitable for pure sine waves. Distorted sine waves can produce considerable deviations.
The VariTrans P 40000 TRMS AC/DC high-voltage transmitters, however, measure the true RMS value (TRMS) of any kind of complex alternating quantities.
Thus, even strongly distorted sinusoidal or pulse-shaped signals are evaluated correctly. Disturbing DC components are not considered.
Crest factor and signal frequency
The crest factor provides a simple means to determine the waveform of a signal. It is the ratio of the peak value to the RMS value of an electrical quantity. The crest factor of a sinusoidal waveform is C = √2 = 1.414.
The measurement range of an AC/DC transmitter is limited by the crest factor and / or the signal frequency. The crest factor of the VariTrans P 40000 TRMS series ranges from 1 to 5.
All power-engineering frequencies, such as 16.7Hz (railway systems), 400Hz (electrical systems of aircrafts and ships), and in particular 50Hz and 60Hz (mains frequency) are processed.
This makes the VariTrans P 40000 TRMS AC/DC high-voltage transmitters suitable for the measurement of even strongly distorted signals. With higher crest factors and/or other signal frequencies, the measurement accuracy will be reduced.
Also in this series, Knick relies on the TransShield technology, which compared to conventional designs enables compact high-voltage transformers with low leakage.
Due to the resulting space advantage, the P 41000 TRMS shunt isolators could be installed in an only 22.5mm wide modular housing.
Another substantial advantage of this technology: high transients (common-mode interference) are reliably isolated and cause hardly any measurement errors at the output.
Calibrated range selection
A highly functional and ideal feature of AC/DC high-voltage transmitters is the calibrated range selection: 16 input/output signal combinations can easily be selected with a rotary coding switch on the front of the device.
Easy scalability of the range selection supports customised solutions; optimally adapted to the respective application, up to 16 tailor-made signal combinations can be implemented in one device.
Integrated broad-range power supply
Maximum flexibility and direct added value for the user is also provided by the integrated VariPower broad-range power supply (20 - 253 V AC/DC).
This ensures trouble-free operation with alternating or direct voltages everywhere in the world and provides for maximum safety even in unstable power supply networks.
Installation is also easy and safe: Incorrect assignment of the mains voltage is practically excluded; expensive downtimes and repairs during commissioning are avoided.
Special vacuum encapsulation protects the circuitry against environmental influences and ensures the high disruptive strength required for working voltages up to 3600V AC/DC.
At the same time, not only the safety regulations stipulated in EN 61010-1, but also the regulations of the EN 50124-1 standard (insulation coordination for railway applications) are observed.
Thus the transmitters are equipped for galvanically isolated measurements of railway transportation systems. To guarantee the specified isolation capabilities, the devices are subjected to routine testing with 15kV AC (fixed-range models) or 10kV AC (switchable models) on a 100% basis.
The vacuum encapsulation technology employed by Knick provides maximum long-term protection against aggressive environmental influences, shock, and vibrations.
Also in the new VariTrans P 40000 TRMS, the circuit design and device construction ensure excellent transmission quality that is reflected in the zero stability, linearity, long-term stability, frequency response, and immunity to interference.
The new AC/DC high-voltage transmitters from Knick accept a wide range of input signals: from a millivolt range – for example for measuring large currents via shunt resistors – to high AC voltages in the kilovolt range.
Currents up to 5A can be measured directly. Analogue unipolar and bipolar (standard) signals are available at the output of the AC/DC high-voltage transmitters.
The user can select any combination of input and output signals and thus take into account the individual operating conditions.
The VariTrans P 40000 TRMS transmitters are ideal for current and voltage measurements in energy networks. Further applications are the monitoring and control of electric drive systems that can be operated at medium or high voltages.
Their sturdy design also makes them suitable for use in rail vehicles. Here, their main tasks include voltage / current monitoring in traction and auxiliary converters.
The high performance and flexibility previously unknown for this device class supports the user in the development of the most diverse product or system solutions.
Optimised product lines
Three product lines in 22.5 to 67.5mm wide housings are offered for different measuring ranges and standard requirements – either as variants with fixed settings or as models with calibrated range selection.
The working voltage for fixed-range models is 3600V AC/DC (test voltage 15kV AC) and 2200V AC/DC (test voltage 10kV AC) for switchable models.
Impressed DC signals 4 - 20mA, 0 - 20mA, or 0 - 10V are available at the output. Customer-specific devices can be equipped with up to 16 freely selectable signal combinations, and even special variants with bipolar output signals and/or high zero offset present no problem.
The Knick high Voltage AC/DC transmitters are available from Alvi Technologies .