This article was originally published on September 26, 2022, and updated on May 8, 2025.
In industries such as oil and gas, chemical processing and manufacturing, maintaining precise pressure control is an important factor in ensuring operational safety and efficiency. A pressure switch is an effective solution to help regulate your system, but its effectiveness depends on the mechanics behind these instruments.
In this article, we will focus on the term deadband and its role in maintaining pressure accuracy in your applications. With Ashcroft's extensive expertise in pressure instrumentation, you will gain insights into optimizing the usage of pressure switches to ensure your systems run smoothly and safely.
When you are finished reading, you will also have access to additional resources to help deepen your knowledge about choosing the right pressure switch for your specific needs.
How a pressure switch works
To understand deadband, you first need to know the basics of a pressure switch.
Pressure switches are devices that make or break an electrical circuit by sensing changes in pressure and mechanically opening and closing a microswitch at a predetermined point. These instruments operate on process pressure rather than electrical power. Here's how they works:
- Process pressure enters the Pressure Connection.
- An increase in pressure applies a force on the Actuator, causing it to move upward.
- The spring and adjusting nut create an opposing force, keeping the actuator from moving up. (Note: the pressure source has to be greater than the opposing force of the spring to move the pushrod and surpass the switch setting.)
- The switch setpoint is controlled by the Adjusting Nut:
Turn Left = Raise Nut = Decrease force = Lower setpoint Turn Right = Lower Nut = Increase force = Increase setpoint - When the force of input pressure overcomes the force from the spring, the pushrod travels upwards towards the Switch Element and trips the microswitch, causing the state of the circuit to change.
Figure 1: How a pressure switch works
What is deadband or hysteresis?
The switch’s setpoint—the pressure at which it activates—is determined by the tension of the spring, which can be adjusted using the adjusting nut. Raising the nut reduces spring force and lowers the setpoint, while lowering the nut increases spring force and raises the setpoint. The switch's reset point is the pressure at which the switch deactivates. Deadband is the difference between the setpoint and the reset point, and is commonly expressed in measurement units of the actuating variable.
Figure 2: Switch deadband diagram
How your pressure switch determines deadband
The type of pressure switch you have will determine its deadband. For instance:
- Fixed deadband pressure switches have a deadband value that is determined by the mechanical properties of the switch, including the rigidness of the diaphragm, the force of the spring and the movement range of the microswitch plunger.
- Adjustable deadband pressure switches, on the other hand, have deadbands that can be adjusted or selected within a specific range to meet your specific application requirements.
Deadband parameters and/or limitations apply to all mechanical pressure switches in all applications.
More about the role of physics in deadband
As we stated previously, pressure switches are mechanical devices, and due to the physics involved, they do not reset immediately after the pressure drops below the setpoint. Switches with an increasing setpoint are activated when pressure rises to the setpoint. However, when the pressure decreases below the setpoint, the instrument does not reset right away. Instead, it requires the pressure to fall further into the deadband zone shown above before it resets.
Figure 3 below demonstrates how increasing pressure compresses the diaphragm and spring, pushing the plunger upward and activating the microswitch. When the pressure drops, the spring force returns the plunger to its resting position, deactivating the switch.
Figure 3: Microswitch activation and deactivation
Figure 4 illustrates a deadband pressure curve. For a switch set at 60 psi with a deadband of 3 psi, the switch will activate at 60 psi as pressure rises and deactivate at 57 psi as pressure falls.
Figure 4: Deadband pressure curve example
Other factors that affect deadband on a pressure switch
In addition to switches with increasing setpoints (those that reset at a lower pressure) and decreasing setpoints (those that reset at a higher pressure), there are a few other factors that influence the size of the deadband. For instance, the force needed to move the microswitch plunger—and thereby the size of the deadband—depends on:
- Spring force (linked to the pressure range)
- Stiffness of the diaphragm material
- Microswitch plunger travel distance
- Design restrictions (e.g., dual microswitch assemblies)
Each of these components contributes to the overall deadband of the pressure switch. How big or small the deadband is depends on these combined factors.
Ready to learn more?
Now that you have a better understanding of deadband for pressure switches, you can make a more informed decision about selecting the best instrument for your application. Here are a few other articles that can deepen your knowledge even further:
- Choosing a Pressure Switch: 9 Factors to Consider
- Choosing the Right Microswitch for Your Application
- Class and Division Codes on Explosion-Proof Pressure Switches
- When Should You Use an Electronic Pressure Switch?
- What is SIL Certification for Pressure Switches?
If you need help finding the right pressure switch for your process, contact us to talk to one of our industry experts and get your questions answered. In the meantime, download our guide to learn how switches can help with chemical and petrochemical applications. 