Pressure sensors are among the most commonly used sensors in industrial practice. They are widely used in various industrial automation environments, including water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military, petrochemical, oil wells, power, shipbuilding, machine tools, pipelines, and many other industries. Therefore, their daily use and maintenance are particularly important. Below, we will introduce them to you in detail.
Unavoidable errors in pressure sensors
When selecting a pressure sensor, we need to consider its overall accuracy. What factors affect the accuracy of a pressure sensor ? In fact, there are many factors that cause sensor error. Below, we will discuss four unavoidable errors, which are the initial errors of the sensor.
Offset error:
Since the vertical offset of the pressure sensor remains constant throughout the pressure range, variations in converter diffusion and laser modulation correction will introduce offset errors.
Sensitivity error:
The magnitude of the error is directly proportional to the pressure. If the device's sensitivity is higher than typical, the sensitivity error will be an increasing function of pressure. If the sensitivity is lower than typical, the sensitivity error will be a decreasing function of pressure. This error arises from changes in the diffusion process.
Linearity error:
This is a factor with a relatively small impact on the initial error of the pressure sensor, which is caused by the physical nonlinearity of the silicon wafer. However, for sensors with amplifiers, the nonlinearity of the amplifier should also be considered. The linear error curve can be either a concave or convex curve for the load cell.
Hysteresis error:
In most cases, the hysteresis error of pressure sensors is negligible because silicon wafers have high mechanical stiffness. Hysteresis error is generally only considered when pressure changes are large.
These four errors in pressure sensors are unavoidable. We can only choose high-precision production equipment and use advanced technology to reduce these errors. We can also perform some error calibration at the factory to minimize errors as much as possible to meet customer needs.
Anti-interference measures for pressure sensors
Maintain stability
Most sensors will "drift" after prolonged use, so it is essential to understand the stability of the sensor before purchasing. This advance preparation can reduce various problems that may arise during future use.
Pressure sensor packaging
Sensor packaging, especially its rack, is often overlooked; however, its shortcomings will gradually become apparent during later use. When purchasing a transmitter, it is essential to consider the sensor's future operating environment, humidity levels, sensor installation method, and the possibility of strong impacts or vibrations.
Select output signal
The required output signal for a pressure sensor—mV, V, mA, or frequency output (digital)—depends on various factors, including the distance between the sensor and the system controller or display, the presence of noise or other electronic interference, the need for an amplifier, and its location. For many OEM devices with short distances between the sensor and controller, mA-level output sensors are the most economical and effective solution. If amplification is required, sensors with built-in amplifiers are preferable. For long-distance transmissions or in the presence of strong electronic interference, mA-level or frequency-level outputs are preferable.
In environments with high RFI or EMI, in addition to selecting the appropriate mA or frequency output, special protection or filters must also be considered. (Currently, due to various data acquisition needs , there are many types of pressure sensor output signals on the market, mainly 4-20mA , 0-20mA , 0-10V , 0-5V, etc., but 4-20mA and 0-10V are more commonly used. Among the output signals I mentioned above, only 2-20mA is two-wire; the number of wires we refer to for output does not include grounding or shielding wires. The others are all three-wire.)
Select excitation voltage
The type of output signal determines the choice of excitation voltage. Many amplified sensors have built-in voltage regulators, thus allowing for a wide power supply voltage range. Some transmitters are fixed-configuration and require a stable operating voltage. Therefore, the available operating voltage determines whether to use a sensor with a regulator. When selecting a transmitter, both the operating voltage and system cost must be considered.
Do interchangeable sensors need to be used?
Determine if the required sensor is compatible with multiple systems. This is generally important, especially for OEM products. Once the product is delivered to the customer, the cost of calibration can be substantial. If the product is highly interchangeable, changing the sensor used will not affect the overall system performance.
other
After determining the parameters mentioned above, we also need to confirm the process connection interface of your pressure sensor and the power supply voltage of the pressure sensor; if used in special occasions, we also need to consider explosion-proof and protection levels.
Pressure sensor routine use and maintenance
To prevent slag from depositing inside the conduit and to prevent the sensor from coming into contact with corrosive or overheated media.
When measuring gas pressure, the pressure tap should be located at the top of the process pipeline, and the sensor should also be installed at the top of the process pipeline so that accumulated liquid can be easily injected into the process pipeline.
When measuring liquid pressure, the pressure tap should be located on the side of the process pipeline to avoid sediment buildup.
The pressure-conducting pipe should be installed in a location with minimal temperature fluctuations.
When measuring liquid pressure, the sensor should be installed in a location that avoids liquid impact (water hammer phenomenon) to prevent damage to the sensor due to overpressure.
When freezing occurs in winter, outdoor sensors must be protected against freezing to prevent the liquid in the pressure inlet from expanding due to freezing, which could lead to sensor damage.
When wiring, pass the cable through the waterproof connector or flexible conduit and tighten the sealing nut to prevent rainwater or other substances from seeping into the transmitter housing through the cable.
When measuring steam or other high-temperature media, a condenser such as a buffer tube (coil) should be added, and the operating temperature of the sensor should not be exceeded.
