Electric Assisted Actuators

The response time of a Caltherm Thermal Actuator will vary with respect to the temperature of the medium in which it is immersed (i.e. air, water, oil, etc.), the load on the piston, and the amount of cup surface exposed. Response time can be controlled to some degree by expansion material formulation. Electrical Assisted Actuators include a resistive heating element as a supplemental heat source which is activated by applying an appropriate voltage and current. The resultant heat causes the expansion material to change state regardless of ambient temperature. When the current is removed the heat source is deactivated, the expansion material cools and returns to its cold state volume. Return springs are used to assist in returning the piston to its start position. The result is a two-position actuator that is controlled by a simple application. It also allows for removal of an applied voltage, similar to an electric solenoid. Therefore, Caltherm's thermal actuators are used to replace simple solenoid functions, especially when high piston forces are required. This eliminates the need for high power requirements and large size envelopes to accommodate the bulky solenoid.

The heat source is an integral part of Caltherm's thermal actuator. It consists of a positive thermal control (PTC) thermistor attached to the bronze cup, which contains the expansion material. Because the electrical resistance of the PTC increases with its rise in temperature, the proper selection of the PTC and expansion material must be made to prevent overheating and over-stroking of the thermal actuator. A PTC's heat source is available in different control voltages (12, 24, 110 and 220 volt). This is usually determined in conjunction with the available voltages in the customer application.

As an added advantage, electric assisted actuators produce piston forces of 270 lbs, with a small power input of 25 watts, silent operation, and small space requirement.