How to select pressure sensor during OEM production
In addition to buying software, the majority of people hope to purchase a suitable OEM products as soon as possible. Finding the ideal pressure sensor is an important part of OEM production. Primarily select on the basis including the following conditions: accuracy, reliability and calibration cycle; operating conditions; contrast and prices of critical and non-critical index .
Original Equipment Manufacturer (OEM) integrate with complex and independent technical for the detection and control of pressure in instrumentation and monitoring equipment. For any OEM design, the main design principle is cost performance of elements, and the pressure sensor and transmitter is one of the price factors to be considered. Generally it’s difficult to obtain satisfactory trade-off. Furthermore, it’s rather difficult to make the right choice for special applications from a variety of pressure sensing technology in the market. At present, the commonly used techniques for pressure as follows: variable capacitor, variable reluctance, eddy current, bonding strain gauge, diaphragm and piezo-resistive silicon technologies.
Variable capacitance sensor is very stable and has excellent characteristics, but requires the media insulating to capacitor element to prevent contamination and moisture.
Rosemount 3051S Series instruments have various variable capacitance pressure sensor, which have a 316L stainless steel chamber with compact structure, water and air sealing, can withstand the harsh field environment. The instrument provides the accuracy of 0.04%, ratio range of 200:1 and 100ms response time. Standard output is 4-20mA signal with HART digital agreement. Foundation fieldbus can be used in the device by upgrading via a simple electronic board. Highly reliable sensors can be installed at the craft field, ruled out the use of power lines, reduce maintenance costs and increase usability.
Variable reluctance and eddy sensor is very suitable for any field of pressure less than 1 psi.
In the vortex pressure sensor, a high-frequency magnetic flux is injected through two coils matching in a magnetic field but not conducting the target. It’s attached to the diaphragm moving along with the differential pressure. The position of the diaphragm can be measured by the magnetic field inducting the difference between the two coils. The built-in electronic component may convert the signals to a standard temperature-compensated output signal.
Due to its measuring range less than 1 in.H2O differential, such products are often used in HVAC systems. Wet / Wet structure is very easy to meet the requirements of the insulating oil. On the downside, these products are generally more expensive and have a larger volume than other sensors.
Bonded strain gauge technology has been applied for over 40 years in our lives, and there are many manufacturers.
Strain gauge sensors, as shown, have two tremendous advantages compared with other pressure sensing technology. Since the strain gauges bonded directly on the sensing film, the film thickness will change according to the changes of the pressure range. Only the bonded metal sheet can measure tens of pounds psi pressure. Because stress film directly bonded to the sensing film, so no need to use an insulating film or rubber filling oil. Therefore, the sensor can easily put off damage of polishing medium (commonly used in the gap of thin film).
These products are moderately accurate, and can not meet the needs of high accuracy. Adhesives used in bonding the strain gauges are limited to normal temperature, and their long-term stability is also a problem. Since the sensing diaphragm of these sensors response time is slowish, they can only be used in water conservancy. In addition, the low price is also their advantage.
The thin film technology has all the advantages of the strain gauge, and greatly improves the long term stability.