Boiler Operator's Guide by Anthony L. Kohan

Author:Anthony L. Kohan
Language: eng
Format: epub, pdf
Publisher: McGraw-Hill Education
Published: 2021-04-15T00:00:00+00:00

Sensors and Controls

All electronics and computer hardware that are involved with controlling a system depend on their performance on the availability of sensors to measure the variables, on their accuracy in getting this information to a computer or programmable controller. There are many physical measurements for which no sensors have yet been developed. One of these, for example, is a continuous readout of the heating value of a fuel. Other measurements must be made to compensate for this so that this information can be used to regulate fuel input to a boiler system.

The arrival of electronic control circuits has seen applications of this technology to boiler controls that are rapidly changing boiler control methods. This is being accelerated by the development of more reliable sensors to detect boiler operating conditions, instruments, and recorders that convert the sensors “reading” into electronic signals that are then transmitted to remote indicators and controllers, as well as being displayed at a central point, such as a control room. With the advent of fiber-optic cables, even longer distance of data transmission is now possible.

Sensors are devices that have the inherent ability to monitor changes in the medium being measured, such as temperature, pressure, flow, level, draft, percentage of CO2, and similar quantities. Sensor wires should not be run in the same conduit as line voltage wires as it will cause interference of the sensor readings and possible false readings. Many boilers have connection ability to the building’s digital control system using either BACnet or LonWorks communication protocols. BACnet means Building Automation and Control Network. LonWorks means Local Operating Network.

Transducers are used to convert the changes noted by a sensor to an electric or a pneumatic signal. These signals are sent to controls, which are set to regulate a quantity within set points. The signals are thus compared to these set points, and if needed, a signal is then relayed to an actuator so that control of the medium is maintained within the established set points. Some controls incorporate the sensor, transducer, and actuator into a self-contained control device.

Figure 10.23b illustrates how one type of device may transmit pressure electrically to indicating, recording, and control equipment at close or remote points by using transmitting equipment and then show measured pressure at that location. The device illustrated has a Bourdon tube that positions a movable core of a transformer from zero pressure to the design pressure. The core position determines the magnetic flux linkage between the primary and secondary windings, which in effect changes the voltage in the secondary with pressure changes. This voltage can be transmitted to standard electronic receivers for further use in control, data recording, computer input, and similar applications.

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