Hysteresis

In the field of temperature regulation, particularly when dealing with thermostat switches, understanding the terms “ON RISE” and “ON FALL” is important. These terms, along with the concept of hysteresis, significantly impact the accurate and reliable operation of these devices.

The Science Behind Thermostat Switches

Thermostat switches control a device by opening or closing an electrical circuit in response to temperature changes. You can use them in various applications, including HVAC systems, food processing equipment, and industrial machinery. For additional information on our capillary thermostats, view the product page.

ON RISE and ON FALL Explained

  • ON RISE: Refers to the point at which a thermostat switch activates (closes the circuit) as the temperature increases.
  • ON FALL: Refers to the point at which the switch deactivates (opens the circuit) as the temperature decreases.

What is Hysteresis?

Hysteresis represents the difference between the activation and deactivation points of a thermostat switch. This difference prevents the switch from constantly toggling on and off in response to minor temperature fluctuations, which could lead to wear and tear or erratic performance.

Practical Example of Hysteresis

Consider a thermostat switch designed to close its contact at 50°F during a temperature rise. As the temperature falls, the switch might not open until the temperature reaches 46°F. In this example, the hysteresis is 4°F. This hysteresis prevents the switch from rapidly toggling between states, enhancing the stability and longevity of the system.

Why Understanding Hysteresis Matters

Understanding hysteresis is important because it affects how you set the operating points of your thermostat switch. If you need the switch to operate at 50°F on a temperature rise, you will need to calibrate it differently than if you need it to operate at 46°F on a temperature fall.

Understanding Bulb and Capillary Thermostats

Bulb and capillary thermostats use the principle of liquid expansion to control temperatures. Here’s how they work:

  • Bulb: Contains a liquid that expands or contracts with temperature changes.
  • Capillary: A slender tube carries the fluid from the bulb to the thermostat’s head.
  • Head: Contains a diaphragm or bellow that moves in response to fluid expansion or contraction, triggering the switch.

When the temperature changes, the fluid inside the bulb and capillary either expands or contracts, causing the head to move and activate a snap-action switch. This mechanism ensures accurate and reliable temperature control.

Understanding the principles of ON RISE, ON FALL, and hysteresis is vital for anyone working with thermostat switches. These concepts ensure that your temperature control systems operate accurately and reliably, avoiding issues such as rapid cycling or inaccurate temperature regulation.

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Bulb & Capillary Thermostats

Original equipment manufacturers worldwide use thermostat switches designed and manufactured by STEMCO, a Division of Senasys. No matter which style or model you choose, all of the capillary thermostat switches operate using the same physics. A fluid is encapsulated in a metal and when the temperature changes the fluid either expands or contracts. This fluid change moves a diaphragm which is in touch with a snap action switch and either opens or closes a circuit.

Ambient Compensation

Our capillary thermostats can be ambient compensated to offset the differential in temperature which keeps our thermostat controls more accurate as it’s environment changes.

Custom Options

Capillary thermostat switches built by Senasys can also be built to customer specifications. This insures you get the exact control you want without paying for features you don’t need.