Pakarab fertilizers limited multan
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- 5.7 Operational Sequences of Three-Valve Manifold Valving Transmitter into Service
| The Receiver Resistor It is much easier to measure a voltage than it is to measure a current. Therefore, many current loop circuits (such as the circuit in Figure 1) use a Receiver Resistor resistor. The current flowing through it produces a voltage that is easily istor, the voltage will be 1 VDC at 4 mA of loop current and 5 VDC at 20 mA of loop current. The most common Receiver Resistor in a 4- 101 Field Instrumentation GEN Rev) 5.6 Three Valve Manifold A three-valve manifold is a device that is used to ensure that the capsule will not be over-ranged. It also allows isolation of the transmitter from the process loop. It consists of two block valves - high pressure and lowpressure block valve - and an equalizing valve. Figure 1 shows a three valve manifold arrangement. 102 Field Instrumentation GEN Rev) During normal operation, the equalizing valve is closed and the two block valves are open. When the transmitter is put into or removed from service, the valves must be operated in such a manner that very high pressure is never applied to only one side of the DP capsule. 5.7 Operational Sequences of Three-Valve Manifold Valving Transmitter into Service To put a DP transmitter into service an operator would perform the following steps 1. Check all valves closed. 2. Open the equalizing valve . this ensures that the same pressure will be applied to both sides of the transmitter, i.e., zero differential pressure. 3. Open the High Pressure block valve slowly, check for leakage from both the high pressure and low-pressure side of the transmitter. 103 Field Instrumentation GEN Rev) 4. Close the equalizing valve . this locks the pressure on both sides of the transmitter. 5. Open the low-pressure block valve to apply process pressure to the low- pressure side of the transmitter and establish the working differential pressure. 6. The transmitter is now in service. Note it maybe necessary to bleed any trapped air from the capsule housing. Download 3.37 Mb. Share with your friends:
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