数字EL定位器英文文献及中文翻译(2)
Moulded coupling version: Ensure coupling is fully engaged before tightening the central screw to close the collet and therefore removing any backlash.
2.2 Mounting of Discrete Positioner
Design and manufacture of the mount kit between positioner and actuator is outside the scope of this document. It is essential that the shaft of the actuator is well aligned with the positioner shaft, and that the two are coupled together with a minimum of
backlash – any backlash acts to deteriorate the performance of the positioner/actuator combination.
It is also essential that the 90 degree travel of the actuator moves the positioner shaft through the correct 90 degree range of travel. The easiest way to ensure that this happens is to mount the discrete unit with the lid and indicator in place – set both the actuator and positioner to mid travel, and mate the two in this orientation. Don't take any chances with this, since misorientation of the positioner shaft and consequent movement beyond its designed range of travel will probably result in damage to the positioner pot drive mechanism. With moulded coupling versions, the Namur drive or Kinetrol square option is an insert in the coupling which can be removed by releasing the central screw.
2.3 Air and Electrical Connections.
2.3.1 Air supply.
Connect air supply (pressure between 3.5 and 7 bar, 50 and 100psi.) to the supply port. It is essential that the air is clean, dry and oil-free. Quality class 6.4.4 (according to ISO standard 8573.2001) is easily adequate – this implies 5 micron max. particle size, 3 deg. C dew point max., and 5 mg/cubic metre max. oil content.
2.3.2 DIN Plug Option.
DIN plug models without the optional limit switches are supplied with only one 4-way DIN plug on the positioner box, and a removable permanent sealing plug covering the second conduit entry, where another DIN plug can be fitted if it subsequently becomes necessary. If a DIN plug model does have the limit switch option, then a second 4 – way DIN plug is fitted; because each limit switch is a 3 terminal device, and there are only two terminals available on the DIN plug for each of the two switches, it is necessary to select normally-open or normally closed function for each switch by connecting the internal wires from DIN terminals A and B to the appropriate terminal inside the box (see Figure 4 above) – the units are supplied connected for normally-open function. If proximity sensors are fitted, then this problem does not arise.
2.3.3 Positioner Signal.
The positioner signal must be 4-20mA. The positioner gives a positioning response between 0 and 90 degrees linearly or non- linearly related to the signal. The positioner is loop powered – that is the signal itself supplies all the electrical power, and no
separate power source is needed. In order to supply enough power, the unit needs between approximately 6 and 8 volts to drive the signal current through it – it behaves electrically like a resistor in series with a zener diode. A typical 4-20mA source with a 24v DC supply is compatible with this input, and can drive a maximum of 2 units in series on one loop.
2.3.4 Angle Retransmit Supply.
The optional angle retransmit circuit is also loop powered, requiring 14 to 30 volts DC to drive the 4-20mA current through it – the current passed is linearly proportional to the actual positioner shaft angle. The retransmit circuit reads the same angle transducing potentiometer as the positioner circuit – however, the angle retransmit circuit remains functional on loss of positioning signal and/or air supply, and the positioner remains functional as long as the signal is present, even if the angle retransmit circuit is fitted and there is no supply to energise its loop. Nevertheless, the angle retransmit circuit is electrically isolated from the positioner signal circuit.
3. SCHEMATIC FUNCTIONAL DIAGRAM.