Sequence controller

Abstract: A built-in insulating element for electrically insulating a process portion (22) from a control object (24) and for transmit­ ting a process result to the control object (24) is provided in the output portion (23) for transmitting the process result of a sequence controller to the control object (24). Further a noise preventive element (9) is provided in the output portion (23) for preventing a noise voltage coming in from the control object (24) side.

Description: BACKGROUND OF THE INVENTION The present invention relates to a sequence controller according to the precharacterizing portion of claim 1 in which a malfunction caused by electrical noises introduced from the outside is prevented. Such a device is known from FR-A-2 607 274. Generally, a sequence controller performs a prescribed sequence process following a sequence program which is set beforehand based on the input data from a control object (external load) showing the external condition, and the process result is output to the control object through an output portion. An electronic circuit such as an arithmetic circuit which constitutes a sequence controller is generally constituted with a TTL circuit, and the signal level is low in the order of 5 VDC. On the other hand, the power supply voltage for signals of a control object such as an external output load or an external input system is so high as 24 VDC or 100/200 VAC, so that when an external signal is made ON, or OFF still higher surge voltage (1 kV to 2 kV) can be induced. To prevent the electronic circuit of a low voltage level from the occurrence of a malfunction affected by a noise voltage of a high level, a control object (external load) and the arithmetic circuit (electronic circuit) of the sequence controller are connected with an insulating element such as a photocoupler. Above-mentioned both circuits are optically coupled for transmitting a process result and also for preventing the noise transmission in the direction of the flow of an ordinary signal by electrical insulation. An according device is described in FR-A-2 607 274. It comprises an input unit, an output unit and a processor unit. The processor unit is electrically insulated from the output unit and input unit. For transmitting commands to the output unit and for receiving data from the input unit optocouplers are provided between processor and unit. Further noise reduction circuitry is employed on the input side. The technique of electrically disconnecting yet optically coupling sub-entity in a circuitry in order to suppress spurious effects is also taken advantage of in an input circuit of a sequencer according to JP-A-59 201 105. In such a sequencer circuit a processor unit having a microcomputer for controlling the external equipment is coupled to the input unit by an optocoupler. Further noise reduction circuitry is then provided between optocoupler and processor. A particular noise reduction circuitry is described in US-A-4 322 771, in which a triac-protected output circuit is contemplated. In the triac-protected output circuit a capacitor is connected across the series connection of a triac and a resistor. This circuitry serves as a snubber circuit, i.e. it filters transients of the voltage supply. The technic mentioned in the above is an effective method for preventing a malfunction of an electronic circuit by cutting off electric noises from control objects, but a surge voltage from a noise generating source is applied to the wirings of control objects through stray couplings in various parts. If the noise voltage is a continuous high frequency pulse-formed high voltage (generally called a burst noise) such as a noise generated when an AC magnet-switch is made off, it comes into an insulating element through stray couplings. In an output portion especially the noise from a control object directly comes into the output side of the insulating element in the direction opposite to that of an ordinary signal flow, which causes the malfunction in the electronic circuit. Because of this, a malfunction can be caused by noise in the output circuit after the insulation element even though a correct process result is transmitted from an arithmetic circuit. SUMMARY OF THE INVENTION An object of the present invention is to provide a sequence controller in which a malfunction is prevented caused by noise transmitted to an output portion from a control object. To achieve the above-mentioned object the sequence controller comprises an input portion which receives input data from a control object, a process portion which processes data according to a sequence program which is set beforehand based on the input data from the input portion, an output portion which electrically insulates the process portion from the control object and also transmits a process result to the control object from the process portion; the output portion has a preventive element for lowering the noise voltage level induced from the control object side. According to the present invention, the noise voltage level which is induced in the opposite direction to that of an ordinary signal flow can be lowered in the output portion, so that it is possible to prevent the malfunction in the output portion. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing an embodiment of the present invention; Fig. 2 is a circuit constitution diagram showing the inside of the output portion of an embodiment of the present invention; Fig. 3 is an illustrative view of the operation principle of the present invention; Fig. 4 is an equivalent circuit for the explanation of operation; Fig. 5 shows the signal waveforms of various parts in the circuit shown in Fig. 4; Fig. 6 shows a characteristic chart of the circuit shown in Fig. 4. DESCRIPTION OF THE EMBODIMENTS The embodiments according to the present invention will be described in detail in the following. In Fig. 1, 20 is a storage portion for storing a sequence program which is set beforehand; 21 is an input portion for receiving the data expressing the condition from a control object 24 as a load; 22 is a process portion for processing the input data from the input portion 21 according to the program stored in the storage portion 20; 23 is an output portion for transferring a control result to a control object 24 receiving the process result of the process portion 22. The part number 1 in the output portion 23 is an insulating element (photocoupler) for electrically insulating the process portion 22 from the control object 24 and also for optically coupling them. The insulating element 1 comprises a light emitting element 1a having a light emission diode and a light receiving element 1b having a light receiving transistor. The part number 9 is a noise preventive element for preventing the noise voltage induced in the output line LO of the control object 24 from being transmitted to the insulation element 23a. An insulating element for electrically insulating the process portion from the control object 24 is included in the input portion 21 though it is not shown in the drawing. In the constitution as shown in the above, there are many kinds of driving equipment to be equipped in the production line and many kinds of sensors for detecting the operating condition of a production line and the operating condition of the driving equipment as control objects 24. A sensor generates input data and sends them out to the input portion 21, and each kind of the driving equipment performs a specified operation receiving a process result etc. from the output portion 23. Detailed description on the output portion 23 is given in the following. In the Fig. 2, 1 is a photocoupler (insulating element) comprising a light emission diode 1a and a light receiving transistor 1b; 2 is a power transistor for amplifying an output signal of the transistor 1b; 3 is a buffer gate; 4 is a flip-flop circuit for storing data; 5 is an external load as control objects comprising L0 to L7, to be concrete they are a driving coil for a magnetic contactor and a motor etc.; 6 is an external power supply for supplying electricity commonly to external loads. A process result (output data) calculated in the process portion 22 is transmitted to the output portion 23 through a data bus 7 and is stored in the flip-flop circuit 4, a storage means of output data, with a latch signal 8 output from the process portion 22. The output data stored in the flip-flop circuit 4 drive the photocoupler 1 through a buffer gate 3. The photocoupler 1 transmits the output signal from the buffer gate 3 to the power transistor 2 after performing electric insulation. The power transistor 2 performs power amplification of the output signal and drives the load 5. The part number 9 is a bypass capacitor as a noise preventive element connected to the output circuit of the light receiving transistor 1b, that is, between the collector and the emitter. The transistor 1b, usually, has stray capacitance between the collector and the base, and the value is 2 or 3 pF. The capacitance of the bypass capacitor 9 is set to be large enough in comparison with the stray capacitance. Fig. 3 is an illustrative drawing showing a way in which a noise is transmitted concerning a control object in Fig. 2. The part number 11 is a noise generating source; 12 is a wiring connected to the noise generating source 11, 13 is the stray coupling capacitance between the wiring 12 and the wiring of the external load 5. When a noise is generated from the noise generating source 11 during the sequence controller is in operation, the noise voltage is applied to the wiring of the external load 5 from the wiring 12 through the stray coupling capacitance 13 between wirings. The noise voltage is applied to the output side of the photocoupler through the wirings in the circuit in the opposite direction to that of the flow of an ordinary signal. To be concrete, the noise voltage is applied between the collector and the emitter (in Fig. 3, the part marked as VCE ) of a transistor 1b for power output. If the bypass capacitor 9 is not provided, as there is a stray capacitance 10 between the collector and the base, the noise voltage is applied to the base from the collector through the stray capacitance 10. When the noise generating source 11 is an AC magnet-switch and the noise is a burst noise such as the one generated when the switch is made off, the noise voltage applied to the base becomes considerably high to flow a base current. As the bypass capacitor 9 is set to be large enough in comparison with the stray capacitance 10, the noise voltage applied between the collector and the emitter of the transistor 1b is bypassed by the bypass capacitor 9, which is easier to pass through than the stray capacitance 10. Therefore, the level of the noise voltage applied between the collector and the emitter can be reduced to be small enough not to be transmitted to the base. It is therefore made possible to prevent the base current from flowing caused by a noise voltage, which prevents the occurrence of a malfunction. In the next step, the description on the safety operating region of the transistor in the photocoupler is given. Fig. 4 is an equivalent circuit of the photocoupler and its output portion shown in Fig. 3. IF is the current of the light emission diode 1a; IC is a collector current of the transistor 1b; VCE is the voltage between the collector and the emitter of the transistor 1b; V is an external power supply voltage; RL is an external load. When the photocoupler is in an OFF condition, that is, when the transistor is in an OFF condition, the capacitor 9 is charged by the voltage V of the external power supply 6 [Fig. 5 (b)], so that the VCE is equal to the voltage V. When the IF starts to flow as shown in Fig. 5 (c) the transistor becomes ON condition and a rush current of IC flows from the capacitor 9 instantaneously. Larger is the capacitance of the capacitor 9, larger is the value of the current, and if the current becomes too large the transistor can be destroyed. Thereby the capacitance of the bypass capacitor shall be set so that the value of IC may not exceed the maximum allowable collector current of the transistor. Because of this, the value of the capacitor C is set to be larger than the stray capacitance between the collector and the base of the transistor and to be not so large as its discharge current destroy the transistor. The rush current as shown in Fig. 5 (a) flows for a time (τ) of a certain time constant. The time constant is decided with the capacitance of the capacitor 9 and an internal resistance between the collector and the emitter. When the current-flowing time (τ) is too long, the generated loss can exceed the allowable collector loss of the transistor and the transistor can be destroyed. Therefore, the capacitance of the capacitor 9 shall be set to have a current-flowing time not so long as to destroy the transistor considering the ratings of the transistor. It is therefore necessary to set the value of the capacitor C to be large enough in comparison with the stray capacitance, and to set the discharge time constant smaller than the value which may destroy the transistor. Fig. 6 is an operation characteristic chart showing the stable operation region of a transistor. In the figure, the relation between IC and VCE when IF is taken as a parameter is shown with a full line, and the allowable collector loss of the transistor when the time constant is taken as a parameter is shown with a broken line. The stable operation region is the space surrounded by a full line, a broken line and the axis of abscissas. PC represents a collector loss. Fig. 5 shows the change of IC and VCE in the ON, OFF operation of the transistor 1b following the ON (emission of light), OFF (no emission of light) of the light emission diode 1a. The operation point at the time of occurrence of IC rush current following the ON operation of the transistor 1b is shown in Fig. 6. In the figure, when the transistor is OFF the operation point is at point P, and when the transistor is made ON to start a rush current, IC is at a peak and the operation point is at point Q, and when the transistor is in a stable ON condition the operation point is at point R, and when the transistor is again made OFF the operation point returns to point P. A proper value of the bypass capacitor 9 is practically in the range of 100 to 10,000 pF. The time constant (τ) in this case is less than 1/1,000,000 sec. In Fig. 6 it is expressed by τ = 0.001 msec., and the stable operation region is broadened to have enough margin, so that it is made possible to prevent the damage to the function or life of the transistor caused by a rush current. In the above-mentioned embodiment, as the base of a transistor for the photocoupler is not used, a photocoupler of four lead wires (2 for a light emission diode, 2 for a transistor) having no base terminal can be adopted; therefore in comparison with a case where a photocoupler of 6 lead wires having a base terminal (1 is blank) is used, mounting density on a substrate etc. can be improved. Besides a photocoupler, a transformer or a Hall element of magnetic coupling type can be used as an insulating element. By a method according to the present invention, the noise resistant capability of a programmable controller against a so called burst noise can be remarkably improved. A method according to the present invention is effective especially for EFT (Electrical Fast Transient) noise test provided in the international standard IEC 801-4.

Claims: A sequence controller comprising: a storage portion (20) for storing a sequence program; an input portion (21) for receiving input data from a control object (24); a process portion (22) for processing data according to said sequence program based on the input data from said input portion (21); an output portion (23) having insulating elements (1) for electrically insulating said process portion (22) from said control object (24), and for transmitting a process result of said process portion (22) to said control object (24) through said insulation elements (1), characterized in that said output portion (23) comprises a bypass capacitor (9) electrically connected between said insulation element (1) and said control object (24) for preventing a noise voltage from said control object (24) side from being applied to said insulation element (1). A sequence controller according to claim 1, wherein in that the insulating element (1) is a built-in photocoupler comprising a light emitting body (1a) and a light receiving body (1b). A sequence controller according to claim 2, wherein said bypass capacitor (9) is provided between the light receiving body (1b) of said photocoupler (1) and said control object (24) for passing noise voltage from said control object (24) side by said light receiving body (1b) of said photocoupler (1). A sequence controller according to claim 2, wherein the light receiving element (1b) is a transistor and the process result of said process portion (22) is transmitted to said control object (24) through the output terminal of said light receiving transistor (1b). A sequence controller according to claim 4, wherein said output portion (23) is so constituted that the process result of said process portion (22) is supplied to said control object (24) through the collector and emitter of said transistor and said bypass capacitor (9) is connected between said collector and emitter. A sequence controller according to claim 4, wherein said output portion (23) is so constituted that said bypass capacitor (9) prevents a noise voltage induced from said control object (24) side from coming into the base through the stray capacitance (10). A sequence controller according to claim 5, wherein said bypass capacitor (9) is set to have enough large capacitance in comparison with the stray capacitance (10) between the collector and the base of said transistor. A sequence controller according to claim 7, wherein said bypass capacitor (9) is set to have a capacitance not so large as to let a discharge current flow to destroy said transistor. A sequence controller according to claim 7, wherein said bypass capacitor (9) is set to have a discharging time constant which is short enough not to destroy said transistor.

Inventors: FUJIWARA KATSUHIRO, OSHIGA TAKAYUKI, UMEDA KAZUNORI, FUJIWARA, KATSUHIRO, OSHIGA, TAKAYUKI, UMEDA, KAZUNORI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1989
Main classification: G05B19
IPC codes: G05B9, G05B19