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Vacuum Gauge Selection Made Easy: Tips and Tricks

When it comes time to choose a new or replacement vacuum gauge for your vacuum pump or system, it is important to take a thoughtful approach. At first glance, it seems a simple task, but you need to consider many factors.

Various factors affect the overall performance/reliability of a vacuum gauge and should be part of the decision process. Each gauge has its own operating range and accuracy level and offers its own advantages and limitations. The following tips will assist you in defining the correct gauge selection for your unique vacuum system.

1.       Understand vacuum design and how does the vacuum gauge work

2.       Know your application for vacuum gauges 

3.       Select the best types of Industrial Vacuum Gauge

4.       Ideal display and scaling

5.       Vacuum installation tricks

6.       Integrating with your system

7.       Cost and maintenance

1.    Understand vacuum gauge design and how does a vacuum pressure gauge work

To determine how to choose the right vacuum gauge, you must understand that most pressure gauges use a bent tube. This tube is called the Borden tube. The tube deflects slightly under the pressure difference between the medium and the atmosphere. 

The tube deflection is converted by the mechanism into the position of the needle on the dial. This design principle is actually the same for normal and vacuum pressure gauges. If you want to learn more about the design principles, you can read our full article on pressure gauges.

Gauges are available with plastic casing or stainless steel. 

Plastic is cheaper and corrosion resistant, but more sensitive to impact. They can be analogue gauges such as Borden tube pressure gauges or digital pressure gauges.

2.    Know applications for vacuum gauges

Practically all industries use vacuum in the automotive industry, food and beverage, construction, pharmaceutical, chemical, marine, etc. Vacuum gauges are important tools for ensuring optimum system performance and safety. It can be used for pick-and-place applications, keeping the workplace clean of contaminants, transporting materials, etc.

·         Vacuum gauge accuracy

Accuracy is the difference between the actual value and the value displayed on the dial. It is usually expressed as a percentage of the period. An accuracy class of 2.5 means that the gauge can deviate from the actual value by up to 2.5%. 

The period of the vacuum gauge is 1 bar (15 psi), this means a deviation of 1 bar * 2.5% = 0.025 bar. Note that temperature fluctuations or heavy vibrations can affect the performance of the gauge. The observer also affects accuracy: reading the dial can lead to small deviations.

·         Pressure gauge for absolute pressure

It is important to note that a vacuum pressure gauge and an absolute pressure gauge are not the same thing. Normal vacuum pressure gauges measure against atmospheric pressure, while absolute pressure gauges measure with respect to absolute zero point. To do this, these gauges have a reference chamber with a nearly perfect vacuum. These are high end products that are used to monitor vacuum pumps or vacuum packaging machines.

3.    Vacuum Gauge types

 Vacuum gauges use a variety of techniques to measure the vacuum in an atmosphere. You can find some of the best industrial vacuum gauge online.

a.    Low vacuum

You can use low vacuum gauge that can be measured through instruments that works on mechanical deflection. Mechanical deflection uses an elastic or flexible element to deflect mechanically with pressure changes, for example a diaphragm, Borden tube or bellows.

·         Piezoelectric pressure sensors measure dynamic and quasi-static pressure. Bi-directional transducer digital vacuum pressure gauges consist of metallized quartz or ceramic materials that have inherently electrical properties. They are capable of converting voltage into electric potential and vice versa. They are very rugged but require amplification circuitry that can be sensitive to shock and vibration.

·         Microelectromechanical systems (MEMS) are microsystems produced by silicon surface micromachining, typically for use in very small industrial or biological systems.

·         Variable capacitance pressure instruments use capacitance changes that result from movement of a diaphragm element to measure pressure. The applied pressure causes the diaphragm to deflect and the capacitance changes. The deflection of the diaphragm causes a change in capacitance which is detected by the bridge circuit.

·         Strain gauges (strain-sensitive variable resistors) are attached to parts of the structure that deform with changes in pressure. Four strain gauges are commonly used in series in a Wheatstone bridge circuit, which are used to make the measurement. When voltage is applied to two opposite corners of the bridge, an electrical output signal develops proportional to the applied voltage.

·         Manometers are usually made of a transparent U-shaped tube and partially filled with a liquid such as water, mercury or oil. The relative amount of fluid displacement between the legs of the U indicates excess pressure on one side or the other. The advantage of using a manometer type vacuum gauge is that the pressure reading is independent of the type of gas.

b.    Medium-high vacuum

Medium to high vacuum needs to be measured using thermal and molecular instruments.

·         A thermocouple gauge measures the change in thermal conductivity of the residual gas within the gauge tube. The pressure reading for this device depends on the type of gas. Thermocouple gauges consist of a filament, a power supply for the filament, and a moving coil meter to display the pressure. 

     The amount of heat lost depends on the pressure of the gas. There are many designs of Pirani gauges. One design involves the use of two plates with different temperatures. The amount of energy expended for heating is a measure of the pressure of a gas. Another design uses a single plate to measure the thermal conductivity of the gas through heat loss to the surroundings.

·         A hot cathode ionization gauge initiates a continuous electron flow from the cathode or electron source to the anode or electron drain. These electrons collide with a pressure-dependent mass of gas molecules, which become positive ions and cause a pressure-dependent current on the ion collector.

·         Cold cathode gauge attracts electrons from the electrode surface through a high potential region.

4.    Display and scale type

 The vacuum gauge has a display that allows the user to monitor the vacuum pressure of the system. Display types include:

·         Analog – Analog meters are simple visual indicators that use a dial.

·         Digital Meter – A digital meter is a numerical valve with a visual indicator.

·         Cathode Ray Tube (CRT) – CRTs are commonly found in computer monitors.

·    Liquid Crystal Display (LCD) – An LCD is a semiconductor light source that uses electrons that recombine with electron holes inside the device and release energy in the form of photons.

·         Multi-Line Video Display – The video display allows the user to view and record a live feed of pressure changes in the system.

·         Single scale instruments display pressure in only one set of units.

·         Dual scale instruments display the pressure in two sets of units on the same dial face.

5.    Installation tricks to improve performance and reliability

The general environment for a particular gauge installation may influence the gauge equipment decision. If the gauge is being installed in a high temperature environment, additional protection of the gauge and possibly an enclosure or modified environment may be required due to the risk of possible ingress of dirt, dust and/or water. 

Also, you need to consider the potential effects of radiation and output signal loss, along with the need to control the gauge from long distances.

If possible, it is recommended to install your gauge in a vertical orientation with 90-degree elbows as close to the chamber as possible to increase overall efficiency and prevent unwanted particles, dust, dirt and moisture from entering the gauge.

6.    Integration with Your System

Each vacuum gauge will output a signal. However, with the proliferation of communication interfaces, knowing which signal is best can be a minefield. The most common applications use a simple 0-10 V analogue signal that can be converted to pressure using a simple equation. This is the least effort way to set up a system, although some industrial applications still use 4-20 mA outputs.

With the increasing need for data collection, digital communication protocols are becoming more common as outputs directly from the gauge head (instead of a hub converter).

7.    Expenses and Maintenance tips

As mentioned earlier, it is important to know what pressure you want to measure, but everyone has a budget. You may be looking at 0.1% accuracy, but it’s worth considering whether you can get 1% accuracy for half the cost. This is why it is so important to understand the actual requirements required for effective monitoring and control of your system.

The main issues affecting cost are accuracy and pressure range:

·         Accuracy – As you might expect, higher accuracy usually brings more cost. It is significantly more expensive than a piezo gauge, especially with a capacitance gauge in rough/moderate vacuums.

·         Pressure range – Two-gauge types are often used together or integrated into one (combination gauge) to measure a wider pressure range, leading to higher costs.

Final thoughts

Vacuums are used in many industrial applications such as automotive, marine, research and development, and manufacturing. 

They can be used to keep materials moving through a system or to keep work areas clear of contaminants. Gauges and instruments, such as sensors, are an important component in ensuring the proper functioning and safety of systems and equipment. All you need is to Buy Industrial Vacuum Gauge Online from a reputed online portal like Emechmart that delivers sturdy and highly durable products.

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