CPI COTI - Heater Circuit - COTI

Secon 11 - Electrical / Electronic Diagrams
11.20 Heater Circuit - COTI
The water temperatures in the Gravity Boiler and the Pressure Boiler (Espresso machines)
are controlled by NTC thermistor probes. They have a variable resistance - high resistance
when cold, low resistance when hot. The thermistor probe is in contact with the water and
connually monitor the water temperature. At room ambient temperature the thermistor
resistance is approx. 3000 ohms. At 205°F the thermistor resistance is approx. 200 ohms.
Both Boiler Heang Elements are controlled by a Solid-State Relay which are in turn con-
trolled from the I/O Board. The Gravity Boiler Element is rated at 1.2kW, and the Espresso
Boiler Element is rated at 1.0kW.
Should control of the Heang Elements fail for any reason, both Elements are protected by
inline reseable Thermal Cut-Outs. These are posioned in the overow pipe of the Gravity
Boiler (176°F), and on the casing of the Espresso Boiler (244°F).
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