Continuous-flow heater with a safety circuit

Abstract

A continuous-flow heater for heating a liquid includes a fluid-accessible channel arrangement with at least one heating channel configured for heating the liquid with at least one electric heating element arranged therein, an electronic control system configured to control electronic circuit breakers in order to electrically operate the heating element and to control the heat output of the heating element, a flow measuring device electrically connected to the electronic control system and configured to detect the volume flow rate of the liquid flowing through the channel arrangement and to provide a pulsed measurement signal, and a safety circuit connected on the input side to the flow measuring device and on the output side to the electronic control system in order to provide a supply voltage for controlling the electronic circuit breakers depending on whether the volume flow rate is greater than a minimum volume flow rate specification.

1 . A continuous-flow heater for heating a liquid, comprising
 a fluid-accessible channel arrangement with at least one heating channel, which is configured for heating the liquid with at least one electric heating element arranged therein;   an electronic control system which is configured to control electronic circuit breakers in order to electrically operate the at least one heating element and to control a heat output of said heating element, the electronic control system being designed as a microprocessor controller;   a flow measuring device, which is electrically connected to the electronic control system and configured to detect a volume flow rate of the liquid flowing through the channel arrangement and to provide a pulsed measurement signal, the number of pulses of the measurement signal correlating to a magnitude of the volume flow rate; and   a safety circuit which is connected on an input side to the flow measuring device and on an output side to the electronic control system in order to provide a supply voltage for controlling the electronic circuit breakers depending on whether the volume flow rate detected by the flow measuring device is greater than a minimum volume flow rate specification.   
     
     
         2 . The continuous-flow heater according to  claim 1 , wherein the safety circuit comprises at least one digital counter having a counter input connected to the flow measuring device, such that the pulsed measurement signal is present at the counter input of the digital counter, wherein at least one counter output of the digital counter is connected to an input of an electronic switching element, which enables or disables the supply voltage for controlling the circuit breakers according to a status of the at least one counter output. 
     
     
         3 . The continuous-flow heater according to  claim 2 , wherein the digital counter has at least one counter disabling input electrically connected to the at least one counter output. 
     
     
         4 . The continuous-flow heater according to  claim 2 , wherein the digital counter is designed as a ring counter. 
     
     
         5 . The continuous-flow heater according to  claim 2 , wherein the digital counter has a reset input, which is electrically connected to a digital output of a triggerably configured monostable multivibrator, wherein a trigger input of the monostable multivibrator is configured to control whether or not a digital level at a digital output of the monostable multivibrator changes once, and wherein a trigger input of the monostable multivibrator is electrically connected to the flow measuring device, such that the pulse measurement signal is present thereat. 
     
     
         6 . The continuous-flow heater according to  claim 5 , wherein the monostable multivibrator is configured in such a manner that the digital level of the digital output changes once as soon as the trigger input is free from pulses of the measurement signal of the flow measuring device. 
     
     
         7 . The continuous-flow heater according to  claim 5 , wherein a time constant of the monostable multivibrator is selected in such a manner that said time constant is a multiple of the maximum pulse length of the measurement signal in each case. 
     
     
         8 . The continuous-flow heater according to  claim 1 , wherein the safety circuit has a digital output which is configured to signal to the microprocessor controller whether or not the supply voltage for controlling the electronic circuit breakers is provided by the safety circuit.