Supply Voltage (Power Supply)
The VariTrans P 15000, A 26000 and P 27000 universal and standard signal isolation amplifiers and the P 40000 series high-voltage isolators are equipped with the VariPower broad-range power supply unit. It is designed for supply voltages of 20 ... 253 V AC/DC. The series P 32000 transmitters can also be equipped with a broad-range power supply. Using this 6-mm broad-range power supply, the transmitters operate at supply voltages from 24 ... 110 V DC and 110 ... 230 V AC.
These isolators and transmitters are therefore suitable for connection to almost all power grids and can be used all over the world. This greatly simplifies warehousing and spare parts inventories.
Another advantage of broad-range power supplies is their insensitivity to power grid fluctuations within the specified ranges. All other Knick isolatorrs and transmitters in modular housings are offered for a standard supply voltage of 24 V DC.
The ZU 0628 DIN rail bus connectors from Knick present a new concept of power supply for modular-housing devices. They are simply inserted in the 35-mm rail. Combined with the IsoPower A 20900 power supply or the ZU 0677 power terminal block, they supply power to isolators and transmitters of the 6-mm series and considerably reduce the cabling effort. Existing systems can easily be retrofitted with these modules.
4.1 Power Requirement
A frequently neglected and often underestimated selection criterion is the power requirement of isolators and transmitters. It is not the additional energy required that is decisive, but the heat generated in the isolators due to the power loss. This disadvantage can have adverse effects especially in the case of high packing densities. Some isolators and transmitters develop so much heat that these devices cannot be mounted next to each other without spacing. Thus the advantage of narrow housings is lost. Another result of high temperatures is the reduced service life of electronic components. A 10 K increase in the operating temperature in the range between 40 °C and 50 °C theoretically causes the service life to be reduced by 50 % and thus considerably lowers product reliability.
The power requirement of isolaors is therefore one selection criterion that should not be ignored. Since the output power of different isolators is generally almost identical, the power requirement of different brands can be compared directly.
4.2 Electrical Isolation of the Power Supply Circuit
3-port isolation is the technical standard for all Knick isolators and transmitters, i. e. the input, output and power supply circuit are galvanically isolated from each other. With 3-port isolators, input and output circuits can be set to any user-defined potential as long as the allowable working voltages are observed. In rare cases where the output has to be set to a higher potential, it is necessary to check whether the allowable working voltage (rated voltage, formerly isolation voltage) across the output and the power supply is sufficiently high.
Some manufacturers who do not supply isolators with 3-port isolation as standard differentiate between input isolators, output isolators, and 3-port isolators.
In input isolators, the input is isolated from all other circuits, the output is at the power supply potential. Input isolators are used to isolate an input signal that is at a potentially interfering or high potential from the output and power supply circuit.
In output isolators, the input is at the same potential as the power supply. The output signal can be applied to another possibly dangerously high potential.
In 3-port isolators, the input, output and power supply circuits are galvanically isolated from each other (see Fig. 20). The input and output circuits can be applied to any potentials, taking account of the permitted working voltages. Differentiating between input and output isolators – as already mentioned above – is not necessary when selecting among Knick isolators, since 3-port isolation is the technical standard here.
Figure 20: Diagram of a typical 3-port isolator