Intelligent pump control
31 August 2009
Vega calls its new Vegamet 391 ‘the latest generation of signal conditioner’ but the instrument is equipped with enough I/O and logic that makes it, in effect, a pump controller. It monitors a single analogue signal (4-20 mA or HART) that represents the level in a tank and makes decisions based on that value. Though it won’t do PID control, it performs on/off control and can also compute flow (with totaliser), distance, weight, and can handle temperature.
‘Not many years ago, this function would have been handled by a small PLC,’ says Vega’s Doug Anderson. If a company only wants to monitor the level in a tank, there are simple scanners available to do the job, he says. The Vegamet 391 does more that monitor as it can perform a certain amount of control on the pumps filling the tank.
Up to six relay alarms can be configured for standard tasks as well as ‘tendency’ monitoring, which is a solution for monitoring remote tanks for theft of product, leakage detection, or linking to a multi-pump system to respond to changes in demand. The controller can be set up so that detects changes in the off hours. Each relay alarm is represented by an LED on the face of the controller.
The ‘Intelligent Pump Management’ (IPM) feature offers two modes of operation, an integrated real-time clock, and six control/alarm relays. IPM allows users to evenly utilise, monitor and control pumps. If one or more of them fails, it can send notification of the failed pump status, and switch to an alternative pump, if one is available. It conforms to the German DIN standard 61132 for pump faults.
Mr. Anderson explains that in some applications, users will have three pumps connected in parallel so they can select one, two, or all three pumps to operate depending on the demand of the system. Normally, when the system is not in high demand, only one pump will be used. The Vegamet 391 can be used to cycle the system to use different pumps, so that the same pump is not continuously being used.
The instrument can also be used as a data logger, so that it can be used for remote inventory data transmission. The user can have any one of a variety of networks: Serial RS232, Modbus TCP/IP, or dial-up. It has integrated web browser, SMS text and email capabilities for values and alarms.
Configuration can be done via the keypad and large back lit graphical display. Alternatively operators can use Windows-based DTM compatible software that is available through Vega, such as PACTware.
Mr. Anderson says that he finds an increasing number of customers are using HART signals, and these have the advantage of transmission up to 1,000 m ‘if the cables are good.’ For larger tank monitoring systems, the company offers the Vegascan which takes in 15 HART signals in multidrop mode.
The Vegamet 391 has an IP65 front facia, ATEX approval and SIL 2 qualification (IEC 61508). Mr. Anderson says that next year, it will be fully SIL 2 qualified with SIL 2 sensors, making it ‘nearly a standalone safety system.’
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