Sharp R-930AW Absolute Humidity Sensor Circuit, Structure of Absolute Humidity Sensor

R-930AK

R-930AW

Pin No.	Signal	I/O	Description
48	P10	OUT	Segment data signal.
			Signal similar to P23.
			Key strobe signal.
			Signal applied to touch-key section. A pulse signal is input to P24-P27 terminal while
			one of G-5 line keys on key matrix is touched.
49-53	P07-P03	OUT	Segment data signal.
			Signal similar to P23.
54-56	P02-P00	OUT	Digit selection signal.
			Signal similar to P55.
57-59	P37-P35	OUT	Digit selection signal.
			Signal similar to P55.
60-64	P34-P30	OUT	Used for initial balancing of the bridge circuit (absolute humidity sensor).

ABSOLUTE HUMIDITY SENSOR CIRCUIT

(1)Structure of Absolute Humidity Sensor

The absolute humidity sensor includes two thermistors as shown in the illustration. One thermistor is housed in the closed vessel filled with dry air while another in the open vessel. Each sensor is provided with the protective cover made of metal mesh to be protected from the external airflow.

		Sensing part	Sensing part
		(Open vessel)	(Closed vessel)
	Sensing part	Thermistor	Thermistor
	(Open vessel)
Ventilation		element	element
openings	Sensing part		Sensor
			case
	(Closed vessel)
View of sensor case removed		Cross section view

(2)Operational Principle of Absolute Humidity Sensor The figure below shows the basic structure of an absolute humidity sensor. A bridge circuit is formed by two thermistors and two resistors (R1 and R2).

The output of the bridge circuit is to be amplified by the operational amplifier.

Each thermistor is supplied with a current to keep it heated at about 150˚C (302˚F), the resultant heat is dissipated in the air and if the two thermistors are placed in different humidity conditions they show different degrees of heat conductivity leading to a potential difference between them causing an output voltage from the bridge circuit, the intensity of which is increased as the absolute humidity of the air increases. Since the output is very minute, it is amplified by the operational amplifier.

				Absolute humidity vs,
C		Operational		output voltage characterist
	R1	amplifier		voltage
			Output
	R2	+	voltage	Output
S		-	S : Thermistor
R3			open vessel
			C : Thermistor
			closed vessel
				Absolute humidity (g/m 2)

(3)Detector Circuit of Absolute Humidity Sensor Circuit This detector circuit is used to detect the output voltage of the absolute humidity circuit to allow the LSI to control sensor cooking of the unit. When the unit is set in the sensor cooking mode, 16 seconds clearing cycle occurs

than the detector circuit starts to function and the LSI observes the initial voltage available at its AN6 terminal. With this voltage given, the switches SW1 to SW5 in the LSI are turned on in such a way as to change the resistance values in parallel with R50-1. Changing the resistance values results in that there is the same potential at both F-3 terminal of the absolute humidity sensor and AN7 terminal of the LSI. The voltage of AN6 terminal will indicate about -2.5V. This initial balancing is set up about 16 seconds after the unit is put in the Sensor Cooking mode. As the sensor cooking proceeds, the food is heated to generate moisture by which the resistance balance of the bridge circuit is deviated to increase the voltage available at AN6 terminal of the LSI. Then the LSI observes that voltage at AN6 terminal and compares it with its initial value, and when the comparison rate reaches the preset value (fixed for each menu to be cooked), the LSI causes the unit to stop sensor cooking; thereafter, the unit goes in the next operation automatically.

When the LSI starts to detect the initial voltage at AN6 terminal 16 seconds after the unit has been put in the Sensor Cooking mode, if it is not possible to balance, of the bridge circuit due to disconnection of the absolute humidity sensor, ERROR will appear on the display and the cooking is stopped.

1) Absolute humidity sensor circuit

		IC2(IZA495DR)						SW1
						4	64
								P30
				620k
						5	63	SW2
								P31
				300k
						6	62	SW3
								P32
				150k
						7	61	SW4
				75k				P33
C. Thermistor in						8	60	SW5
				37.4k				P34
closed vesssl
S. Thermistor in
open vessel						3	5	AN7
			47k	F	∝F
						F
				∝
				0.01	0.015	∝		LSI
F-1	11					0.01
C								(IC1)
F-3	3.57k		+		10k
						2	6
S			0.1 F∝			47k		AN6
	3.32k		-
F-2			1.8k
	10			360k
	R51	9
				12		1
VA : -15V			VA : -15V		VC : -5V

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