As more systems benefit from microprocessor-based controls, many system developers are now able to a specify pressure sensors into applications that have previously used pressure switches. Incorporating a sensor instead of a switch allows systems to be more efficient and offers the user more features and flexibility. A pressure sensor provides a linear dc output voltage change that is proportional to the pressure applied. This allows for a calibrated, accurate output voltage to be provided over the entire pressure range that a system might experience.
Pressure switches typically provide only two output voltages, on or off, corresponding to a specific pressure point. In many cases the “switching” point is not nearly as accurate as a sensor and can drift over time and with thermal exposure. Additionally, the accuracy of the switching pressure is typically not better than 3 percent of the maximum pressure value applied. In contrast, a pressure sensor typically provides accuracies of 1.5 percent (of pressure span) or better and over a broad thermal range of 0 to 100C.
The sensor output also offers resolution down to 0.025 percent, providing the system developer expanded flexibility in control or trigger points. In theory, a developer could design in as many switching points that are needed with one single sensor. More advanced systems can be designed to measure the rate at which pressure is changing to accelerate a system's response to the changing condition.
Several control systems rely on accurate pressure sensors to perform properly. In the HVAC industry, pressure sensing is relied upon for control of the refrigerant during the compression and expansion phases of the media. Over the years this industry has developed more energy-efficient, modulated systems that can operate in several modes to allow rapid change as well as low demand, sustained control. This could only have been accomplished with the integration of a pressure sensor.
In the transportation arena, one area that has benefited from converting from switches to sensors is that of air filtration, specifically for heavy-duty on- and off-road vehicles. Historically, pressure switches have been used to signal when an air filter is clogged and needs to be serviced. New systems are now using pressure sensors to allow the pressure drop across a filter to be used for more than just filter condition. Now, the rate at which a filter becomes clogged can be monitored and used to offer other diagnostic features with respect to engine health.
Kavlico produces a wide variety of pressure sensors that can provide a calibrated output voltage directly to a microprocessor-based system. For low to medium gage pressure applications, Kavlico's P4055 product family can easily be integrated into most pressure systems and is available with several pressure fitting options. The P4055 product family uses piezo-resistive-based sensing technology. The sense element is bonded directly to a thick film screened ceramic hybrid that contains the entire compensation and amplification circuit. With the entire sensor circuit on one hybrid, a high level of reliability is realized from the minimum number of circuit interconnects. This product family is available in pressure ranges up to 300 psi or 20 bar.
As system developers are presented with the challenge of providing more capability with less cost at the same time as having their next-generation systems consume less energy, many will turn to the advantage that pressure sensors will offer over the old switch approach. Simply dusting off the old idea will not work anymore ... when all is said and done, it's time to lose the pressure switch and start converting to pressure sensors for a more cost-effective and efficient measurement approach.