METHOD FOR CHECKING HARDNESS SENSOR

PURPOSE:To make it possible to decide normal/abnormal of a hardness sensor by a constitution wherein a decision unit monitors the output from the hardness sensor in relation to the opening/closing of a channel to the hardness sensor. CONSTITUTION:Raw water from a raw water supply line 2 is subjected to softening by a water softener 1 thence fed through a soft water supply line 3 to cooling and heating machines. In this regard, a first valve V1 is opened whereas a second valve V2 is closed. Under that state, a decision unit C monitors the output from a hardness sensor S constantly. Upon elapse of a predetermined time, the valve V2 is opened and the processed water is partially fed from the water softener 1 to a measuring vessel 5 through a hardness measuring line 4. After the valve V2 is opened, the hardness sensor S measures the hardness of the processed water and it the output from the sensor S varies, the decision unit C makes a decision that the sensor S is normal. An alarm is delivered when the output from the sensor S represents a hardness higher than a set value.