Effective, profitable power plant operation requires managing capital-expense turbine, boiler, and combustion equipment, along with many other assets that must be balanced precisely. Reliable readings of pressure, temperature, and other process variables are critical to success.

While analogue transmitters are known for accuracy and reliability, maintenance costs increase with age and flexibility for performance improvement is limited. To reduce long term operating costs and maintain quality service to its more than 300,000 customers, a Michigan power utility launched a programme to replace its aging analog transformers with modern digital transmitters.

The utility uses transmitters for draft indications on the boiler and pulverised mill area. They read pressure on the boiler, the turbine, combustion, and steam heating equipment. Some of the instruments send data to a centralised distributed control system (DCS), which manages the set points that control the sensitive interactions. Other instruments simply indicate various pressure states to operators and maintenance technicians.

When this power utility implemented its first DCS, all transmitters were analog. At the time, mixing and matching multiple brands of analog sensors was difficult, and in some cases impossible, because of proprietary mounting configurations. Management at this Michigan power plant wanted to be certain that they chose a digital sensor that would not lock them into a single vendor.

After evaluating transmitter suppliers, the utility selected Foxboro intelligent instrumentation with standard mounting configurations. And Invensys Process Systems' ability to guarantee quick delivery further supported the decision to purchase Foxboro transmitters.

Thus far, Invensys has supplied differential pressure and gauge pressure transmitters to the power plant. The Foxboro IDP10 is an intelligent two-wire differential pressure transmitter with high-performance accuracy to + 0.05 per cent of calibrated span. The IDP10 provides measurement spans of 0.12 to 21000 kPa (0.018 to 3000 psi), which expands its versatility so that a single transmitter can satisfy nearly all DP applications.

The Foxboro IGP10 is a two-wire transmitter for high gauge pressure applications to 52, 105, or 310 MPa (7500, 15,000, or 30,000 psi). Gauge pressure measurement spans may be as low as 0.12 kPa (0.5 inH2O) to as high as 35 MPa (5000 psi).

The Foxboro IDP10 and IGP10 pressure transmitters are available with 4 to 20 mA analog output, as well as HART, FOUNDATION Fieldbus, PROFIBUS, and FoxCom communications protocol compatibility. These transmitters are also available with industry standard and are backed with an industry-leading standard five-year warranty mounting configurations that make it easier and less expensive to replace existing transmitters and reuse existing installation designs without being limited to a single supplier.

Ease of calibration is another major benefit that the power utility receives, since the Foxboro digital transmitters can be calibrated by using either the push buttons on the digital transmitter's LCD, a handheld communicator, a notebook/desktop computer, or from the operator station of the DCS.

The transmitters' standard mounting configuration, which serves as a universal replacement for all competitive models, allows the power utility to change transmitters without having to replace the entire manifold. Likewise, if they want to replace a transmitter and do not happen to have the primary vendor's product available, they now have the flexibility to use another brand.

The power utility has also realised increased productivity resulting from less calibration. With analog gauges calibration was frequent and time consuming. The digital transmitters require calibration considerably less often, which is usually done during forced outages.

The ease of making routine calibrations has had a true preventive maintenance benefit as well. By being able to check and correct calibration on every instrument during a shutdown, plant operators are more confident that all instruments will be operating at peak performance once the system starts up.

The utility has also benefited from Invensys rapid order fulfillment. To take advantage of a scheduled shutdown, they needed the first 90 transmitters within four days. Invensys and the local representative committed to meeting their immediate deadline and delivered on their promise. And last year the utility installed another 90 or so transmitters and timing was even more of an issue. Invensys once again came through.

Invensys Process Systems