Various pressure gauges in the measurement industry
A gauge is essentially an instrument or device used to measure the size, quantity, or content of something, usually with an analog or digital display. This can be a measurement of any property, such as pressure, flow, temperature, fuel, or length. In the field of measurement and instrumentation, the word "gage" is often used as a variant spelling of the word "gauge".
As the name implies, a pressure measuring instrument is a tool used to measure and indicate the pressure of a liquid or gas inside the system compared to an atmosphere or another reference. There are many types of pressure gauges available, each using a different technique or method of indication.
Analog pressure gauge
An analog pressure gauge usually refers to a device that uses pure mechanical pressure sensing technology. The measurement value is indicated by the movement of the pointer on the dial, and each pressure value is marked. Pointer The movement and position of the pointer give a visual indication of the pressure being measured.
Most analog pressure gauges have one of the following three pressure sensing technologies:
Bourdon tube
The Bourdon tube is a "C"-shaped, spiral-shaped or spiral-shaped radially formed tube, one side of which is fixed at the bottom of the instrument, and the other side is connected to the pointer. When the Bourdon tube is compressed, its cross-section tends to become more rounded, thereby tending to straighten the shape. This movement of the tube is captured by the pointer to indicate the pressure. The Bourdon tube pressure gauge is the most common type of analog pressure gauge in the industry, with various pressure ranges, pointers and Bourdon materials. The dials and hands of the intuitive display are usually liquid-filled or vacuum-sealed to reduce noise in various applications.
Learn more about WIKA Bourdon regulations
Diaphragm
The diaphragm pressure gauge contains a wave-shaped diaphragm that is connected to the pointer using a linkage mechanism. Pressure is applied to one side of the diaphragm, which is usually enclosed by a flange. The movement (expansion or contraction) of this diaphragm is captured by this link and transmitted to the pointer to indicate pressure. The different surface areas of the diaphragm can provide different levels of sensitivity. For example, a diaphragm with a large surface area will provide higher sensitivity and is common in many low-pressure applications. In addition, especially for corrosive media, the diaphragm and flange will prevent the measured medium from entering the sensing device. This is why diaphragm pressure gauges are very popular in applications that require lower pressure or corrosive media.
Learn more about the advantages of diaphragm pressure gauges
Bellows
The corrugated tube is a one-piece foldable device with deep folds or crimps formed by extremely thin-walled tubes. When pressure is applied or released to the inside of the bellows, it will contract and expand respectively. This movement is then transmitted to the pointer via the link. Similar to diaphragm pressure gauges, bellows with larger diameters are most suitable for low pressure and provide higher performance accuracy. Generally, the number of folds of bellows varies from 5 to 20, but due to their length, they are limited in terms of the maximum pressure that can be achieved.
Digital pressure gauge
Simply put, a digital pressure gauge is a device that digitally displays pressure output through a screen installed on its body. Generally, digital pressure gauges use electromechanical pressure measurement in their housing and a circuit that converts this value into a display reading. The digital output usually allows the operator to easily record pressure readings at a higher resolution than the analog output. Digital meters require a power source (usually in the form of batteries) to operate and power internal sensors and displays.
Generally, digital pressure gauges have one of the following technologies:
Strain gauge sensor
The working principle of the strain gauge sensor is to convert the applied pressure into an electrical signal through the elastic deformation of the strain gauge. These strain gauges are connected to the main body of the measuring device and arranged side by side to form a Wheatstone bridge circuit. When pressure is applied, the strain gauge will elastically deform, thereby changing the resistance of the strain gauge and the bridge circuit. This change in resistance produces an electrical output signal that is proportional to the amount of pressure applied to the meter.
Piezoelectric sensor
The word "piezo" comes from piezein, which is a Greek word that means one form of physical pressure or another. Piezoelectric sensors use piezoelectric materials such as ceramics and quartz crystals. The dynamic pressure acting on the crystal generates an electric charge, which is amplified and converted into a voltage or frequency signal. Unlike strain gauge sensors, piezoelectric sensors do not require external excitation. However, the biggest problem with piezoelectric sensors is that the crystal generates electric charge only when dynamic pressure is applied, and it is only in a dormant state under steady-state conditions. There are many ways to package piezoelectric sensors to reliably read static pressure, but these methods may involve additional diaphragms and the use of pre-tightening screws to compress the crystal, resulting in expensive and sensitive meters.
Piezoresistive sensor
Piezoresistive-based transducers rely on the piezoresistive effect, which occurs when the resistance of a material changes in response to an applied mechanical strain. Piezoresistive sensors are usually made of MEMS (Micro Electro Mechanical System) silicon components. This is mainly due to the fact that silicon has a piezoresistive effect that is two orders of magnitude larger than that of metal, which results in a pressure measurement output with higher accuracy and resolution. Unlike strain gauges and piezoelectric sensors, piezoresistive sensors use a single material (silicon) to achieve uniform thermal characteristics and predictable and reliable temperature performance. Piezoresistive sensors are one of the most common sensors for accurate pressure measurement in applications that require extensive and reliable temperature compensation. CPG1500 uses an internal piezoresistive sensor. Its resistance is converted using the onboard computer and displayed on the screen.
