Detecting apparatus using a digital computer

A detecting apparatus for compensating for changes in supply voltage to a physical parameter sensor. The apparatus includes an input element, such as a heatsensitive resistor connected to a voltage source to produce a voltage signal (C.sub.S) corresponding to a physical factor, e.g., a temperature. A constant voltage circuit or a voltage divider connected to the same voltage source as the input element produces a reference voltage signal (C.sub.R) corresponding to a predetermined reference value of the input element. Both voltage signals (C.sub.S, C.sub.R) are applied to a microcomputer in which a correction value (C.sub.C) is calculated on the basis of the both voltage signals (C.sub.S, C.sub.R) and a theoretical set value (C.sub.O) of the reference voltage signal (C.sub.R). The detected physical factor by the input element is corrected by the correction value (C.sub.C).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to a detecting apparatus using a 
digital computer, and more in particularly to a detecting apparatus for 
rendering a control specification to coincide with a standard 
specification. 
2. Description of the Prior Art 
In a detecting apparatus using a digital computer, the resistance value of 
a heat-sensitive resistor or a variable resistor or the value of the 
electromotive force of a piezoelectric element used as an input element is 
provided usually as a converted value of a predetermined range of 
voltages, so that the A/D converted digital value of the voltage is used 
to determine the input condition of the digital computer thereby to 
control an output element. The characteristic variations of the individual 
elements directly affecting the voltage conversion, however, present 
themselves as variations of the control specification of a final product, 
and therefore, the variations of the control specifications are required 
to be held within a predetermined tolerance by preshipment adjustment. 
In a widely-used method, the characteristics of the input elements, namely, 
the relation between the physical factors and the value of a generated 
voltage is adjusted within the range of the standard characteristics by 
use of a variable correction resistor or a pre-amplifier with the gain 
thereof controllable. 
The greatest disadvantage of this method is that a considerable number of 
adjustment steps is involved. 
SUMMARY OF THE INVENTION 
In view of the above-mentioned fact, the object of the present invention is 
generally to simplify the adjusting work and to reduce the steps of the 
adjusting work, and specifically to provide a control system in which in 
order to maintain the control specification within a standard or reference 
range, a control digital computer has an adjusting function by a 
calculation based on the program thereof, thus eliminating the need of 
adjustment of the input element itself. 
As described above, according to the present invention, there is provided a 
detecting apparatus comprising a reference voltage source for correction 
under the control of the same power supply as an input element, means for 
converting the voltage generated from the input element into a digital 
value and means for correctional calculating by use of the reference 
voltage from a reference voltage source. This eliminates the need of 
manual adjusting work thereby to greatly reduce the number of steps for 
producing the control system. Further, the adverse effect of such vague 
variable factors as the change with temperature or time can be dampened.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A part of a control system for an air conditioner is shown in FIG. 1 as an 
embodiment of the present invention. Reference numeral 1 designates a 
transformer for dropping the voltage of a commercial power supply, numeral 
2 a rectifier circuit using a diode bridge, and numeral 3 a 
constant-voltage circuit with its output source voltage expressed as Vcc. 
designates a microcomputer (such as M58840 of Mitsubishi Electric 
Corporation) includes a central processing unit (CPU) (not shown), a 
read-only memory (ROM) (not shown), a random access memory (RAM) not 
shown, and an A/D converter 4a, input ports I.sub.1 . . . I.sub.5 and an 
output port O.sub.1, a heat-sensitive resistor 5 for generating an analog 
voltage V.sub.1 corresponding to the temperature of the space controlled, 
and a variable resistor 6 for setting a control target temperature, which 
applies a setting voltage V.sub.4 to the input port I.sub.4 of the 
microcomputer and the voltages V.sub.3 and V.sub.5 of junction points of 
the clamp resistors R.sub.3 and R.sub.4 across the variable resistor to 
the input ports I.sub.3 and I.sub.5 respectively. A constant-voltage 
circuit 7 is provided for generating a reference voltage V.sub.REF for 
used by A/D converter 4a in microcomputer 4 and for applying the reference 
voltage V.sub.REF to the reference voltage input terminal of the 
microcomputer. Reference characters R.sub.1 and R.sub.2 designate fixed 
resistors for applying the voltage V.sub.2 to the input port I.sub.2 for 
correcting the voltage produced from the heat-sensitive resistor 5. The 
resistance value of the fixed resistors R.sub.1 and R.sub.2 is selected in 
such a manner as to produce a voltage equal to the voltage V.sub.1 of the 
heat-sensitive resistor 5 at a reference temperature (which is assumed to 
be Ts). 
Numeral 8 designates an output relay connected to the output port O.sub.1 
of the microcomputer 4. Numeral 9 designates a motor compressor for the 
air-conditioner which is connected to a contact 8a of the output relay 8 
and operated and stopped by the output of the microcomputer. Output 
elements other than the compressor will not be described. 
A flowchart generally showing a control program of the microcomputer 4 is 
shown in FIG. 2. The correctional calculation is always made during the 
execution of the program. 
A detailed flowchart of the correctional calculation program is shown in 
FIG. 3. 
A method of adjustment will be described below with reference to the 
flowchart of FIG. 3. FIG. 3 corresponds to the "correction calculation" 
block shown in FIG. 2. In the case where the source voltage V.sub.CC and 
the reference voltage V.sub.REF for A/D conversion take theoretical 
values, the A/D converted value of the voltage V.sub.1 generated at the 
ambient temperature of Ts of the heat-sensitive resistor 5 is assumed to 
be C.sub.T. Generally, the temperature Ts is selected to be a middle point 
of the control temperature range. Assuming that the A/D converted values 
CV.sub.1 and CV.sub.2 are applied from the input ports I.sub.1 and 
I.sub.2 respectively and that the value CV.sub.1 is corrected to obtain 
the value CV.sub.1 ', the correctional calculation is given by the 
equation (1) below. 
EQU CV.sub.1 '=CV.sub.1 +(C.sub.T -CV.sub.2) (1) 
The values V.sub.CC and V.sub.REF are not necessarily coincident with the 
theoretical values thereof due to the variations of the elements involved. 
Thus, in the case where the value CV.sub.2 is larger than the theoretical 
value C.sub.T, the correction is made to reduce the value CV.sub.1 ', 
whereas in the case where the value CV.sub.2 is smaller than C.sub.T, the 
correction is made to increase the value CV.sub.1 '. 
Now, let us assume that the A/D converted value of the voltage V.sub.1 at 
the theoretical value To of the target temperature is Co when the variable 
resistor 6 is set at the middle point. Also assuming that the A/D 
converted values of the voltages applied from the input ports I.sub.3, 
I.sub.4 and I.sub.5 are CV.sub.3, CV.sub.4 and CV.sub.5 respectively, and 
that the corrected value of CV.sub.4 is CV.sub.4 ', the correctional 
calculation is expressed by the equation (2) below. 
EQU CV.sub.4 '=CV.sub.4 +(Co-(CV.sub.3 +CV.sub.5)/2 (2) 
As in the case of the correctional calculation of the voltage CV.sub.1, the 
correction is made to reduce the value CV.sub.4 ' when the value (CV.sub.3 
+CV.sub.5)/2 is larger than the theoretical value Co, whereas the 
correction is made to increase the value CV.sub.4 ' when the value 
(CV.sub.3 +CV.sub.5)/2 is smaller than the theoretical value Co. 
The theoretical values CT and Co in the abovementioned correctional 
calculations are defined as a constant in the program. These values are 
not limited to a hypothetical middle point in a control range or the 
middle point of a variable resistor but may be defined at an appropriate 
value. In this case, the voltage-dividing ratio of the resistors R.sub.1 
and R.sub.2 may be changed or the variable CV.sub.2 in equation (1) or the 
variable (CV.sub.3 +CV.sub.5) in equation (2) may be multiplied by an 
appropriate ratio (constant). 
A specific calculation procedure of equations (1) and (2) above is 
appropriately set by a given combination of commands provided in the 
computer 4 and may be arranged in the significance indicated by the 
equations (1) and (2) respectively. 
As shown in FIG. 2, the control system, namely, the air conditioner is such 
that in the case where the room temperature is higher than a set 
temperature on the basis of the value obtained by the correctional 
calculation, the output port O.sub.1 is turned on while in the case where 
the room temperature is lower than the set temperature, the output port 
O.sub.1 is turned off in order to control the compressor. 
Each time the correctional calculation routine is passed, the A/D 
conversion is effected and a new correction value is calculated to be used 
for control. As a result, even under the operating conditions where the 
stabilization voltage V.sub.CC or V.sub.REF is changed by the change of 
the characteristics of the constant-voltage circuit 3 or 7 against 
temperature or the like, an always correct digital value of the physical 
quantity which should be exhibited by the input elements 5 and 6 is 
grasped for operation of the control system. 
The aforementioned embodiment concerns the correction of temperature and a 
set temperature. The present invention may be further applied to the 
discrimination of the operating mode as shown in FIG. 4 where the 
operating position of an operating mode change-over switch is determined 
by use of a single input port I.sub.6 from the difference of the divided 
voltage, in a manner similar to the correction shown in equation (1). 
Furthermore, a similar correction is possible also in a microcomputer 
having an A/D converter as an external element. 
The present invention may also be applied to the case where a piezoelectric 
element or a differential transformer is used as an input element.