Electronic Pressure Switches - Term Paper Example

Module: The electronic pressure switch Introduction The measurement of pressure using electronic devices usually contributes to the safety, accuracy and saving of energy in various process. Together with measurement of temperature, pressure measurement is the most important and most common technology in the monitoring and control of plants and machinery. Pneumatics and hydraulics in particular, the measurement and control of the pressure of the system is a crucial prerequisite for an operation that is both safe and economic (Terry 2006). In the past 20 years, the measurement of pressure using electronic devices has been integrated into a number of applications and more continue to be added each day as technology advances. Various devices have been developed to cover the various applications and users have a multitude of instruments to choose from. The selection is normally based on the comparison of various parameters and a weighting of the requirements in relation to each other. This is important to ensure that maximum safety of operation is ensured and also that the planned performance of the plant and machinery is achieved (Dale & Erik, 2011). This helps to reduce the overall cost of performance. Discussion In various applications, electronic pressure switches normally replace the use of mechanical pressure switches which used to be very common. Due to their design principle and additional functions such as digital display, switch points that are adjustable and higher reliability, they offer better reliability (William, 2004). Electronic pressure switches are mostly used in machine building. Electronic pressure switches are based on an electronic pressure transmitter and thus offer all the functions offered by a transmitter. The main elements of the electronic pressure switch include the following: The switch, a pressure transmitter and a digital indicator all integrated into one single component. Figure 1: Electronic pressure switch 1. The switch This element is integrated into the pressure switch and it is able to close and open an electrical circuit and it is thus making the devices capable of performing simple control tasks. Both the switch point and the reset point can be set individually and by default, the pressure switch can only output binary signals and as a result many switches have an additional analogue output signal (Dale & Erik, 2011). This allows for the set parameters and the measured pressure to be read off display. The analogue output signal also allows for the measured pressure to be transmitted to a downstream control unit. 2. Pressure transmitter The pressure transmitter has an interface that is standardized on both the side that does the signal processing and other side that outputs the electrical signal and converts the value of the physical pressure into a standard industrial signal. The connection is normally used to lead the pressure directly into the sensor and has a standardized thread and an integrated sealing system in order to enable easy connection of the standard instrument and the functionality of the switch. In devices that have an analogue output, the transmitter allows for the transmission of the electronic signal to the analogue display device (William, 2004). 3. Digital indicator This component allows for the display of the signal. The standardized signal is displayed on the screen. The display screen is mostly LED but with the development in technology, more complicated display units are being integrated into these devices. Other special features can be available in various electronic pressure switches depending on the main application of the device. Some of these features include: piezo resistive sensor and the thin film technology, programming menu and a user friendly 3 key operation (Terry 2006). Figure 2: Block diagram of the electronic pressure switch Properties A number of errors are can be experienced during the operation of this device and these include: non-linearity, hysteresis, span error and non-linearity. If the instrument used in measuring the pressure is operated at a constant temperature, then the maximum error is maximum. 1. Non-linearity This is the measuring error normally defined as the largest possible either positive or negative deviations. Non linearity is a basic characteristic that can be seen in the sensors used in the device and it can be minimized in the electronic device by the manufacturer 2. Hysteresis This refers to the maximum deviation that is realized between the increasing and decreasing characteristic curves. It is dependent on the elastic properties of the sensor materials and the principle used in the design of the sensor. This effect cannot be adjusted by any technical form of measurement. 3. Total band error Both the actual zero and the end point of the output signal may deviate from the ideal zero point and end point. The zero offset and span errors realized in the device are usually the differences in values between the ideal and the actual values of the zero point and end point of the output signal. In rarely extreme cases, both values can provide the same preceding sign thus producing the maximum error value in the same pressure measuring instrument (Terry 2006). 4. Temperature error Any change in temperature normally influences the measurement related characteristics directly of the electronic device. An increase in temperature increases the electrical resistance of metals and increasing the piezo resistance of the semi-conductors.in order to minimize this effect, manufacturers normally take a number of measures related to the sensor system and the associated electronics. This optimizes the sensor design (Terry 2006). With the exception of hysteresis, these errors can be minimized by taking corresponding measurements. Data accuracy Data accuracy is normally determined through statistics. This is because the measuring errors are both systematic and random in nature. A maximum error in this device is normally plus or minus three times its standard deviation. Device specifications 1. Measuring accuracy Deviation Read More