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HabiStat Pulse Proportional Thermostat
The function of this thermostat is far more sophisticated than the simpler on/off switching devices. It will very accurately control heaters and has a maximum load capacity of 600 watts. A regular thermostat switches a heater on at full power until the set temperature is achieved. It then switches the heater completely off until the temperature drops below the set value, when the cycle starts over again. The gap between the heater being switched on and then off is called hysteresis. It is between these points that the accuracy of the controller is assessed. The pulse proportional thermostat pulses electricity to the heater.
How a pulse proportional thermostat works.
The temperature is set on the dial. The cage and heater are cold so the heater is switched on to full power. Power is supplied to the heater in a cycle of pulses, the more pulses there are in a given cycle the more energy is supplied to the heater. At full power the whole of the cycle is taken up by pulses. As the temperature in the cage nears the set temperature the unit cuts the power to the heater down to fewer pulses per cycle. The amount of pulses per cycle is dependent on the set temperature.
At the set temperature the amount of pulses in the cycle will exactly match the amount of energy needed by the heater to maintain the heater at that value. The heater is neither on nor off but supplied with the appropriate amount of power it needs to do its job. Should the cage become warmer or cooler the sensor will detect the change and adjust the amount of power to correspond to the new situation.
As a rough guide the proportion of the cycle delivering energy should be approximately 50%. This will indicate the relative suitability of a heater to a given situation. If the pulsing, as indicated by the neon on the heater, is about 50% on and 50% off then the heaters power rating is about right. If the neon is on for most of the time, is shows the heater is struggling and probably needs to be changed for a more powerful model. Conversely, when the neon spends more time off than on, the heater may be too powerful for the cage it is being asked to heat.
In any case, the heater is only powered enough to maintain the temperature set. It does not have to continually start the heater from cold. This vastly improves heater element life and is far safer for the animals, as the heater rarely, if ever, needs to run at full power.
Night time temperature drop facility
This facility is available as an option on both the Pulse Proportional and Dimming Thermostats. With many species, it is important to give them a cycle of warm day time and cool night temperatures. Many species would experience this in their natural environment.
Through an additional mains input lead and via a HabiStat Magic Eye or a time switch, the thermostat will lower the set temperature for the period of time set on the time switch. This temperature drop can be adjusted to be anything from approximately 5C to 15C lower than the day time set temperature. This drop is obviously dependent on the ambient temperature where the cage is kept. The temperature cannot drop below this without the aid of a chiller.
How the night time drop facility works.
The thermostat is functioning normally and the set temperature of 28C, as an example, is being maintained. A secondary mains input via a time switch is set to turn on at 8.00 p.m. The night time drop facility is set at a mid way point to give a drop of approximately 7C.
At 8.00 p.m. the time switches in a second mains feed which sets a new set temperature of 21C. Assuming the ambient temperature is lower than this, the thermostat then maintains the heater at the night time temperature of 21C. The off time for the time switch is set at 7.00 am. When the timer switches off at the end of the night period the thermostat reverts back to control the day time set temperature at 28.
In a correctly set up cage, with the size heater matched to the size of enclosure and temperature required, the heater will run at part power all the time. If the dimming thermostat is being used to control a primary basking spot for example, the heater should provide a small spot of fairly intense local heat. A large and powerful heater would be dimmed down to quite a low level, not what is wanted in a basking light! Clearly, the precise requirements of the heater need to be considered. In this case, reducing the size of the heater so that the wattage is less and the intensity of heat is proportionally localised. |
