Evolution Technical Manual - Jemphrey

Technical Manual
11.17 Heater Circuit
Please refer to diagram on page 124.
1. The water temperature in the heater tank and pressure boiler(B2C machines) is
controlled by the thermistor probe. The thermistor has a variable resistance -
when cold it has a high resistance and when hot a low resistance.
2. The thermistor probe sits directly in the water and continuously senses the water
temperature. The resistance of the thermistor is interpreted by the controller as
a temperature reading.
N.B. The resistance of the thermistor when at ambient (room) temperature
should read approximately 3000 ohms. When hot (96°C) it should read
approximately 220 ohms.
3. If the water needs to be heated, a signal from the controller is sent down the
Comms. link to the I/O board (heater on signal). The I/O board then switches a
24 volt negative output to the solid state relay. This in turn switches a 240 volt
supply to the heater element which heats the water.
N.B. The heater element fitted to the heater tank is rated at 2.4kW. The element
fitted in the pressure boiler (B2C machines only) is rated at 2kW.
4. This process continues continues until the water has reached the temperature set
in the temperature configuration program.
5. If the water in the heater tank should overheat and boil over, a high temperature
cut out, positioned in the overflow pipe, will cut off the mains supply to the heater
at approximately 90°C within 60 seconds.
6. When the maximum temperature (set in the temperature configuration program)
has been reached the ‘heater on’ signal is removed from the Comms. link
switching off the 24 volt negative output from the I/O board, the solid state relay
and the heater element.
7. B2C Machines: Whenever an espresso based drink is selected, the water is
heated in the pressure boiler throughout the vend.
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