Products Service Applications Blog & Wiki Downloads About us Careers News & Events
Untitled-design-1

5 tips and tricks for choosing the right vacuum gauges

December 14, 2021

7 min read

When it's time to select a new or replacement vacuum gauge for your vacuum pump or system, it's important to take a thoughtful approach. At first glance, it might seem like a simple task, but there are several factors you need to consider. 

Various factors affect a vacuum gauge’s overall performance/reliability and must be part of the decision process. Each gauge has its own operating range and accuracy level and offers its own sets of benefits and limitations. Looking at the following tips will help you define the right choice of gauge for your unique vacuum system.

  1. Operating vacuum level and accuracy

  1. Process/application impact on the gauge  

  1. Ambient conditions  

  1. Interface to your system

  1. Cost and maintenance

Vacuum gauge options

Before diving into these main options, let’s investigate gauge types. There are two main types of vacuum gauges: direct and indirect.

Direct gauges

Direct gauges will give you the pressure of the vacuum system, independent of gas type (therefore also known as gas independent gauges). These will only effectively work at pressures above 10-4 mbar. This is because they rely on the molecules in the system having a physical effect, and at lower pressures, there are not enough molecules to have a measurable effect. They include:

  • Piezo – an accurate measure of vacuum and overpressure down to around 1 mbar (below 1 mbar accuracy tends to drift)

  • Mechanical Dial – visual indication of the pressure (useful in applications for local display)

  • Capacitance – highly accurate, capable of measuring from atmosphere to 10-5 Torr (measures 4 decades with extreme accuracy within top 2 decades) 

Indirect gauges

Indirect gauges often rely on two measurement technologies: thermal conductance or ionization. Both measurement technologies are dependent on the gas type; therefore, knowing what gas you are measuring is important if you want to know the true pressure. By knowing the gas type, you can apply a gas correction factor. These gauges fall into three main types:

  • Pirani (Thermal gauge) – used in rough to medium vacuum, often as a low-cost alternative to Piezo/Capacitance gauges where accuracy is less important

  • Cold cathode (Ionization gauge) – used in medium to high vacuum for indication of pressure (robust technology for high particulate applications)

  • Hot Cathode (Ionization gauge) – used in medium to ultra-high vacuum, higher accuracy, and wider measurement range compared to cold cathode technology, drawbacks include it requires slightly higher power and it is more sensitive to vibration/shock and air inrush, but it’s really good for clean, high vacuum applications  

Active and passive gauges

With indirect gauges, there is another subsection: active and passive.

Most gauges you see on the market are active, with embedded electronics to do the signal processing and give a 0-10 V or other analog output proportional to the pressure. However, in environments with large amounts of radiation, the active sensors are affected and not reliable. In these circumstances, you can get versions of the gauges with the electronics removed and put in the controller, which can be positioned away from the radiated area for optimum performance.

 

1. Operating vacuum level and accuracy

Vacuum level is perhaps the most critical consideration. Vacuum level affects each of the other factors, and typically, you need a gauge that measures within your operating pressure range. Typical classifications and ranges include:

  • Rough vacuum: from above atmosphere to 1 mbar

  • Medium vacuum: 1 mbar to 10 -3 mbar

  • High Vacuum: 10 -3 mbar to 10 -9 mbar

Different gauge technologies are required to achieve different vacuum pressure ranges. Depending on the target vacuum level, a mix of gauges might be necessary to get measurements across the entire pumping range. 

Rough/medium vacuum gauges — There are many options, and with both direct and indirect options available, knowing the process requirements is vital for choosing the right gauge

High and ultra-high vacuum gauges — There are slightly fewer options with the area dominated by either hot cathode or cold cathode type gauges (both of which are indirect gauges)

image-png-Dec-13-2021

Vacuum level is perhaps the most critical consideration. Vacuum level affects each of the other factors, and typically, you need a gauge that measures within your operating pressure range. Typical classifications and ranges include:

  • Typically, gauges operating in rough to medium vacuum have higher accuracy than those operating in medium to ultra-high vacuum. Direct gauges are more accurate than indirect. Direct gauges usually have an accuracy of between 0.2 to 2%, with their accuracy decreasing as the pressure drops. Indirect gauges generally vary between 10% and 30% depending on the gauge technology but have consistent accuracy across their ranges.
  • Therefore, depending on what you are intending to use the gauge for, you need to choose the right gauge to cover your operating pressure and desired accuracy. 
     
    Explore the Leybold range of precision vacuum gauges and controllers on our product page. 

2. Process or Application Impacts on Gauge

The way processes can impact gauges plays a significant role in selection. The impact of the application on the selected gauge technology needs to be evaluated carefully, as well as the potential impact of:

  • Dust or debris from the process

  • Corrosive gases like chlorine or acidic mixtures in the presence of water vapor

  • Frequent venting

  • Vibrations

  • Particle or X-ray radiation

  • Magnetic and electric fields

For example, Pirani gauges are well-suited for many rough and medium vacuum applications, such as:

  • Research and development

  • Analytical instruments

  • Industrial and coating activities

  • Freeze-drying

  • Process engineering 

On the other hand, Capacitance gauges provide high accuracy in a specific range of vacuum by electrically measuring the small deflections on a diaphragm membrane caused by fluctuations in vacuum levels. However, with great accuracy comes an increased cost. That’s why it is so important to know what you require from your measuring system. 

3. Ambient conditions

The general environment for the installation of a particular gauge can impact the decision of gauge equipment. If the gauge is being installed in a high-temperature environment, the risk of dirt, dust, and/or potential ingress of water could lead to the need for additional protection of the gauge and possibly an enclosure or a modified environment. Also, you need to consider the potential effects of radiation and output signal loss with the need to control a gauge from long distances.

4. Interface into your system

Every vacuum gauge will output a signal. However, with the proliferation of communication interfaces, it can be a minefield knowing what signal is best. The most common of applications utilize a simple 0-10 V analog signal that can be converted into a pressure using a simple equation. This is the lowest effort way of setting up a system, although some industrial applications still use a 4-20 mA output.

With the increasing need for data collection, digital communication protocols are becoming common as a direct output from the gauge head itself (instead of via a hub converter). The requirements include RS232/RS485, EtherCAT, Profibus, Ethernet IP, etc.

5. Cost and Maintenance

As mentioned earlier, knowing what pressure you want to measure is important, but everyone has a budget. You may want 0.1% accuracy, but if you can get 1% accuracy for half the cost it may be important to consider. That’s why it’s so important to understand the actual requirements needed to monitor and control your system effectively.

The main points that influence costs are the accuracy and pressure range:

  • Accuracy – as you’d expect, high accuracy usually drives higher costs. This is especially true when in rough/medium vacuum with Capacitance gauges being significantly more expensive than Piezo gauges.

  • Pressure range – to measure across a wider pressure range two-gauge types are often used together or integrated into one (combination gauge), leading to a higher cost. 

Tricks for installation to improve performance and reliability

Recommendations

If possible, it’s recommended to install your gauge in the vertical orientation with a 90-degree elbow as close to the chamber as possible to increase the overall performance and to keep unwanted particulate, dust, dirt, and moisture from entering the gauge. It’s also important to install your gauge 90 degrees from any inlet purge gas or vent stream (see sketches below):

 

Recommended:

image-png-Dec-13-2021
Image 5
Image 3

Not Recommended:

Image 6
Image 4
Image 2

Final thoughts

I hope these Five Tips and Tricks for choosing the right vacuum gauge will help you make the right decision when choosing an effective gauge for your application. A better understanding of your vacuum pump and/or system requirements like pressure range, accuracy, control requirements, and cost impacts will help you make the right decision. You can view our gauges here in our eShop.

Leak Detection - banner

Leak detector 101

Download our e-Book "Fundamentals of Leak Detection" to discover leak detection essentials and techniques.

Leybold employee

Let's talk

We focus on customer proximity. Contact us for all your questions.

Contact us

Loading...