At the data acquisition level the system uses only high performance pressure transmitters (PT) from reputable vendors. The pressure transmitter selection takes into consideration the application requirements and constraints. We usually deliver Emerson 3051S as a good, proven solution.
Pressure transducer installation should meet the following demands:
- The pilot pipe may not be thinner than 25 mm / one inch
- The pilot pipe should not be longer than 3 meters. Longer pilot pipe, what may be necessary because of pipeline burial depth, should be 50 mm / two inches wide.
- Special measures against the risk of vaporization of the media under the transducer body must be considered - vent valves and fixing of the leading pilot pipe from the pipeline side.
- The length of the signal cable is limited to 1500 m (via current loop 4-20 mA) or 400 m (communication bus).
The LDS measurement station requires a power supply in the range from 24VDC to 110 or 230 VAC. The power consumption of a measurement station depends on its design (mostly on the presence of heating module); anyway, it will not exceed 40W if supplied from external 24VDC. PAS can also provide an off-grid solution, based on a proven combination of two solar panels and a wind turbine.
The measurement station also requires the GPS time synchronization, which means there must be a possibility for GPS antenna outdoor installation, under the open sky.
PAS company can provide the communication system, based on a cellular network 3G/LTE modems. Quite often we also use the existing communication like FOC, metallic cable or radio modem. The data exchange between LDS measurement stations and the central part is small in the volume and frequency - one measurement station should have the refresh period of 20 to 120 seconds, while the data will be less than 100 bytes per message.
The controllers have three communication interfaces by default: two RJ45 Ethernet ports and one RS232 serial port. Expansion modules like RS422/485/CAN are available as an option.
There are two possible scenarios for communication system architecture:
- the measurement stations are connected by a direct link to the central station
- the measurement stations exchange data with local SCADA station, which transfers LDS data together with SCADA data in one packet to the center; at the center the SCADA system exchanges data with LDS central station.
In any case, the communication system must be bi-directional, as the central station sends requests (containing a few NPW parameters) and the measurement station answers with a reply. This request-reply schema is applied to each measurement station, the central station being a master.
The communication system must be transparent, with no buffering.