In many areas of applications the use of shunt resistors has established itself as a reliable, precise and long-term stable solution for continuous measurement of DC current. The low voltage drop across the shunt resistor is directly proportional to the flowing current. It is sensed by a specially designed shunt isolator, where it is converted to a standard signal and output as a measure of the current for further processing in controllers or displays.
DC currents are measured in a diverse range of applications, including photovoltaics, power supply of public transport systems, control of motors and generators, DC busses of inverters, welding equipment, and generally in systems with high DC currents.
The currents to be measured are associated with system voltages (potentials) which must be safely separated, i.e. galvanically isolated by the shunt isolator. Here, it is important that the voltage measurement is not affected by common mode influences. This can be achieved even for shunt voltages as low as 60 mV by suitably designed shunt isolators. Higher shunt voltages are not necessary with high-quality shunt isolators and because of the physically larger shunt resistors they are generally not desired.
Particularly for high currents, the loss in the shunt resistor must be very low to prevent excessive heating. In any case, the resistance of the shunt should be as constant as possible with changing temperatures. The shunt resistor must be insensitive to corrosion or other environmental effects. Here, special attention must be paid to material and workmanship.
Maconic shunt resistors are the result of many years of experience in the design and production of such resistors. They are carefully manufactured using high-quality materials. The resistor bars are made of manganin, a special manganese-copper-nickel alloy, so that a very low temperature coefficient is achieved.
Dimensioning and mechanical construction are such that the resistors only moderately heat up until the rated current is reached.
The shunt resistors and associated shunt isolators achieve a very good long-term stability, which guarantees the specified accuracy over the normal periods of application of many years. Current peaks do not cause any offset or drift.
Protection equipment based on current measurement benefits from the reliability and long-term stability of the measurement and achieves a particularly high level of safety performance.
Due to the low shunt voltage of 60 mV, the dimensions of the shunt resistor can be comparatively small – and this is not at the expense of measurement accuracy because the shunt isolators from Knick are optimized for their special task.
Safe measurement of currents associated with high system voltages up to the kV range is also possible.
The 3-port-isolated transmitters provide a correspondingly high galvanic isolation and are rated at 3.6 kV working voltage / 15 kV test voltage.