TM 10-7310-241-12&P Change 1     1-13/(14 blank)           1-14.  HWR FUNCTIONAL DESCRIPTION (Continued)      e.  Boil-dry Sensor.  Temperature-dependent network that directly monitors the heater temperature and outputs a corresponding signal to the boil-dry detector. The sensor is mechanically a part of the heater for Model RAK-15. f.  Boil-dry Detector.  Monitors the output from the boil-dry sensor and activates the heater off latch when the signal represents a heater temperature of 490 ^oF (255 ^oC) for Model RAK-15. g.  Heater Off Latch.  Electronic circuit that is enabled by the V+ supply when the LO/OFF/HI switch is set to LO or HI. In operation the circuit is latched "off" to disable the heater control circuit and thereby prevent heating operation if the power supply is less than 22 V dc or if the internal temperature is greater than 205 ^oF (96 ^oC) for Model RAK-15, or 20 V dc, or if the internal temperature is greater than 239 ^oF for Model 471012.   NOTE If the circuit has been latched in the "off'” condition it will need to be "unlatched" by first setting the LO/OFF/HI switch to OFF (to remove the V+ supply) then reselecting the LO or HI heating range as required. h.  POWER ON Lamp.  Green LED that lights to provide visual indication the power supply is turned on when the LO/OFF/HI switch is set to the LO or HI position (Model RAK-15) or setting I (low) or II (high) for (Model 471012). i.  LO Sensor.  Temperature-dependent network which provides a control input to the heater control circuit when selected via the LO position of the LO/OFF/HI switch (Model RAK-15) or the I/0/II switch for (Model 471012).  The sensor measures thermal feedback from the outer container and thereby maintains the internal temperature within the LO heating range. j.  HI Sensor.  Temperature-dependent network which provides a control input to the heater control circuit when selected via the HI position of the LO/OFF/HI switch (Model RAK-15) or the I/0/II switch for (Model 471012).  The sensor measures thermal feedback from the outer container and thereby maintains the internal temperature within the HI heating range. k.  Power Switch.  Operator-controlled 3-position toggle switch with a center OFF position.  Selects a heating range of 150 -160 ^oF (66 - 71 ^oC) when the setting is LO or I or a heating range of 180 -190 ^oF (82 - 88 ^oC) when the setting is HI or II.  If the power supply is turned on, the switch also lights the POWER ON lamp and enables the heater off latch when set to the LO or HI (I or II) position. I.  Heater Control.  Electronic circuit that normally provides on/off relay switching of the heater in response to the control input received from the LO or HI sensor via the power switch (i.e., acts as a thermal servo). The circuit can also be disabled by the heater off latch or the overheat sensor in order to prevent heating operation under abnormal conditions (Model RAK-15). m.  HEATER ON Lamp.  Yellow LED (Model RAK-15) or white LED (Model 471012) that lights to provide visual indication that power is being applied to the heater. n.  Heater.  Comprises a 28 V, 15 A heating element, which supplies conductive heat to the outer container when power is applied from the heater control circuit. The heater is protected by a non-repairable thermal fuse that operates at a temperature of 374 ^oF (190 ^oC)  (Model RAK-15). o.  Overheat Sensor. The temperature-dependent network that monitors conductive heat from the outer container and disables the heater control circuit. If the temperature rises above a level of 205 ^oF (Model RAK- 15) or 239 ^oF (Model 471012). The action is delayed for a short period of time (approximately 20 seconds) in order to prevent spurious operation.