OHD3-75B

OHD3-75B is a mechanical thermostat that is used to detect temperatures and make decisions on when to turn on parts or systems in various applications. This thermostat is sometimes referred to as a snap-disc, snap-action, or bimetal thermostat. OHD3-75B thermostats have two different types of applications and they use a different working principle depending on the application.

General Purpose Applications

The OHD3-75B is used in general purpose applications to provide protection against temperatures going beyond a certain limit. In these applications, the thermostat is used to provide an automatic shutdown if a device or system exceeds a preset temperature. The thermostat acts as an over-temperature trip and can be used to protect devices from damage caused by excessively high temperatures.

The thermostat is most effective in general purpose applications when it is used in a closed system, where it is electrically interconnected with the system\'s control circuit. The electrical circuit has two sets of leads that connect the thermostat to the system. One set of leads is used to provide power to the thermostat, while the other set enables the thermostat to control the system through an open/close mechanism.

In general purpose applications, the thermostat works by using a bimetallic spring strip that expands when heated. The expansion of the strip causes the contacts of the thermostat to open, interrupting the power to the system and shutting it down. The thermostat is precisely calibrated to stimulate expansion of the bimetallic strip at the exact temperature required by the system.

Heat Pump Applications

The OHD3-75B thermostat is also used in heat pump applications to provide the signal to change from cooling to heating cycles, or vice versa. In this application, the thermostat works in a similar way to the general purpose application. However, the two sets of leads on the thermostat are not used as power leads, but instead are used to open and close the heat pump\'s reversing valve. This is done by providing an open or close signal to the reversing valve, depending on which cycle the system is in.

The thermostat works in heat pump applications by using a bimetallic strip just like in general purpose applications. However, the difference in this application is that the strip is calibrated to control the supply low-voltage signal. When the bimetallic strip is activated, it sends a signal to close or open the reversing valve, forcing the heat pump to switch between heating and cooling mode.