JPS6115442B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is an on/off device that performs on/off operation in response to changes in state values such as temperature, humidity, or pressure.
The present invention relates to an off adjustment circuit. General on/off control circuits have a fairly large switch differential in order to achieve operational stability, so the meaning of the control function is lost in systems where the state value changes extremely slowly. . For example, if we take the temperature control of a refrigerating case installed in a supermarket as an example, the indoor air temperature is kept low even in the summer by air conditioning, so the condition value rises and the refrigerating machine stops operating. Once started, this operating state continues for a long time, and frost formation often occurs during this time. When frost forms, cooling efficiency decreases, requiring longer operation times, and defrosting with heaters results in wasteful energy usage. SUMMARY OF THE INVENTION An object of the present invention is to provide an on/off adjustment circuit that operates in response to slight fluctuations in state values and that does not repeat unstable on/off cycles. Next, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, resistances R1 to R
3. A bridge circuit consisting of a status detector such as a resistance temperature detector RT, a variable resistor VR as a setting device, and a power source E is connected to a point a connected to the slider of the variable resistor VR and a connection point between resistors R2 and R3. An output voltage proportional to the resistance value of the resistance temperature detector RT (ie, the temperature around it) is generated between the series of points b. This output voltage is then supplied directly to the first comparator 1 and to the second comparator 2 via the resistor R4. The upper operating points of comparators 1 and 2 are almost equal to each other, but
The lower operating points are approximately equal to each other, but the lower operating points are different. In this example, by setting the positive feedback amount of the first comparator 1 to an appropriate value, the lower limit operating point of the first comparator 1 can be set to be equal to the desired setting value SP, or by setting it to a certain value. is set to a lower value. The resistor R6 and diode D2 shown in FIG. 1 provide hysteresis between the upper limit operating point and the lower limit operating point of the first comparator 1. On the other hand, the lower limit operating point of the second comparator 2 has a differential like that of a normal thermostat. Note that resistance R5
and diode D1 constitute a positive feedback loop of comparator 2. Furthermore, a timer circuit 3 is provided which performs a timer operation depending on the output state of the first comparator 1. This timer circuit 3 is reset when the output of the comparator 1 becomes H, and when it becomes L, the reset operation is shifted to the counting operation and a predetermined timer operation is started, and when the set time elapses, the timer circuit 3 is reset. Output B from L level to H
level and holds this state until the next reset. The NAND gate 5 has an output A obtained by inverting the output of the first comparator 1 with an inverter 4, and an output B of the timer circuit 3.
is input, and outputs Y such that both of them are at H level. On the other hand, the second comparator 2
The output of is inverted by the inverter 6 and becomes the output X. And the outputs Y and X are the NAND gate 7
is input. Therefore, the output Z of the NAND gate 7 becomes the L level only when the outputs Y and X are both at the H level, and this is taken out as an on/off output. The signal processing circuit for this output Z can be easily constructed by, for example, a relay circuit. FIG. 2 shows the operating state of each part when the value of the process variable PV (temperature in this case) that changes the resistance value of the resistance temperature detector RT changes. This operation diagram assumes temperature control in a refrigerating case installed in a supermarket, for example, and stops the operation of the refrigerator when the output Z is H, and stops the operation of the refrigerator when the output Z is L. I am planning on doing it. In the process of increasing the PV value, in a section a where the value is lower than the set value SP, the output of the first comparator 1 is L, and the output of the second comparator 2 is H. In this state, the timer circuit 3
is in a timing or hold state, so its output is either L or H. Therefore, the output Y can take either H or L value, but since the output of the second comparator 2 is H and therefore the output X is L, the output Z is the value of the output B of the timer circuit 3. It is always kept at H, regardless of the Next, when the PV value exceeds the SP value, that is, in the case of a refrigerated case, when cooling becomes necessary, the output becomes L, and therefore the output X becomes H. Also, since the output becomes H, the output A becomes L, and at the same time, the timer circuit 3 is reset in response to the H level output, and if the output B is H at this time, it immediately becomes L.
As a result, both outputs A and B become L, output Y becomes H, and output Z becomes L. That is, operation of the refrigerator is started. This state is maintained during section b until the PV value becomes lower than the lower limit operating point of the first comparator 1. When the PV value becomes lower than the lower limit operating point of the first comparator 1, its output changes from H to L, thereby causing the timer circuit 3 to start a predetermined timer operation. When a predetermined set time has elapsed, the timer circuit 3 changes its output B to H, thereby causing its output Y to become L. That is, after the period c corresponding to the set time of the timer circuit 3 has passed, the output Z becomes H again regardless of the level of the output of the second comparator 2. That is, the operation of the refrigerator is stopped, and therefore the V value is in the interval d.
It will rise as shown in . And again
When the PV value exceeds the SP value, the output Z is set to L as described above and the refrigerator starts operating.
This is section e. Output in each section a to e, A, B, Y, X
and Z levels are shown in Table 1 below.

[Table] In other words, sections a, b, c,
The following points become clear from d and e. (a) Since the conventional on/off adjustment circuit only controls the on/off of comparator 2, V
The value snakes between the differentials of comparator 2, and the range of change in the PV value becomes large.However, according to the present invention, the PV value reaches the lower limit of the differential of comparator 2. Since the refrigerator is configured to be stopped before and returned to the SP value, it will be set near the SP value. That is, control characteristics are improved. (b) As a reflection effect of this control characteristic, if only the comparator 2 is controlled on/off, Z continues to be L in the section d. In other words, the refrigerator continues to operate even though the PV value is far different from the SP value and it is cold. In contrast, in the present invention, Z in section d becomes H, and the refrigerator is not operated unnecessarily. In other words, energy saving control can be realized. Furthermore, in the present invention, even if there is a sudden change in the PV value in a time shorter than the timer time, the control characteristics will not deteriorate compared to on/off control using only the comparator 2. Next, this point will be explained using section f in the operation diagram of FIG. The section f assumes a situation where the PV value reaches the lower limit value of the differential of the comparator 2 within the timer time due to some condition. At this time, the output of comparator 2 is H
, so X becomes L, and therefore the output Z becomes H
Stop refrigeration operation. That is, since the refrigeration operation is stopped regardless of the mode of timer output B, excessive refrigeration will not occur. In addition, comparator 1, 2 differential,
The set time of the timer circuit 3 can be arbitrarily set according to various conditions such as the characteristics of the state detector or the form of the controlled object. As described above, in the on/off adjustment circuit of the present invention, the output control signal is determined according to the magnitude of the state value with respect to the set value, and when inverting from one value to another value, the output control signal is determined by the setting of the timer circuit. This is done after a lapse of time, and the reversal is instantaneous. Therefore, hunting does not occur even if the differential of the comparator is almost zero. It also has a normal differential function, so that if the state value crosses the switch point before the set time of the timer circuit has elapsed, the output control signal can be inverted.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an on/off adjustment circuit according to an embodiment of the present invention, and FIG. 2 is a graph showing changes in the output state of each part of FIG. 1 with respect to changes in state values. 1, 2...Comparator, 3...Timer circuit, 4~
7...NAD gate, RT...resistance temperature sensor.

Claims (1)

[Claims] 1 A state detection circuit, a setting circuit, a state value detected by the state detection circuit and a setting value set by the setting circuit are compared, and the controller is turned on in order to make the state value match the setting value.・Second set with a differential in the setting value that sends out the off output
a first comparator that receives the set value as an input and sets a differential limit value between the set value and the differential limit value of the second comparator; A comparator is provided, and the operation is started when the state value deviates from the set value and reaches the limit value of the differential of the first comparator, and the operation device is not operated within a predetermined time from the start of the operation. and a timer circuit that outputs a command signal for forcibly converting the output of the first comparator to a signal for driving the operating device, and the output of the second comparator and the command signal. An on/off adjustment circuit comprising: an AND circuit that drives the operating device when the outputs of the first comparator to be converted are both in a mode to drive the operating device.