A critical measurement for a power plant is the amount of steam being sent and billed to its customers.
The above system uses a vortex flow meter for volume measurement of the steam flow. The meter’s 4 to 20 mA output is sent to a flow computer. A pressure transmitter output and an RTD output are also sent to the flow computer.
The computer applies the three inputs in a mass flow equation and displays the resulting mass flow rate in pounds per hour and a total in pounds supplied. The rate and total are corrected for any changes in the temperature and/or pressure. This method insures an accurate steam flow and total measurement because it is pressure and temperature compensated.
The system is powered by an uninterruptible power supply that insures that the steam flow measurement continues even when main line power is not available. Audible and visual alarms are also included to warn the control room and local personnel about loss of power to the system and any out of normal parameters, such as high flow, no flow, high or low temperature or pressure, etc.
In addition to the computer's standard 4 to 20 mA output, a modem is also connected to a phone line via an RS232 connection for remote monitoring from a central office location.
Isolation valves between the pressure transmitter and the main steam line are used to isolate the transmitter for calibration or service.
As an option, a multi-variable differential pressure mass flow transmitter can also be used to measure pressure and temperature compensated steam flow. The transmitter includes a static pressure and RTD temperature measurement. When combined with a differential pressure from a differential pressure device like an orifice plate or an annubar, the transmitter microprocessor can produce a steam mass flow measurement. Other methods of communication such as ethernet and wireless are also available.
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