JPH03126101A - Input circuit for programmable controller - Google Patents

Abstract

PURPOSE:To easily design a system by providing a constant voltage circuit, which stabilizes the input signal voltage to a certain voltage, to eliminate a need to select an input module in accordance with the input voltage. CONSTITUTION:An input circuit 1 of a programmable controller is provided with a constant voltage circuit 10 which stabilizes the input signal voltage, whose maximum is at least four times as high as a prescribed voltage, to a certain voltage. Thus, the heat generation from resistances R2 and R3 provided on the output side of the constant voltage circuit 10 is not increased but the power consumption of a control transistor Q of the constant voltage circuit 10 is only increased in proportion to the input voltage when the input voltage is increased, and one input circuit is shared among plural kinds of input voltage. The current for signal input is fixed to easily determine a circuit constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an input circuit for a programmable controller, and particularly to an input circuit for a programmable controller that can easily cope with changes in input voltage.

[Conventional technology]

2. Description of the Related Art Programmable controllers (hereinafter abbreviated as PC) are used to control various industrial machines, either as stand-alone controllers or as built-in numerical controllers.

The input circuit receives signals indicating the status of the controlled object and operation command signals from the operator, and converts them into digital signals at a predetermined voltage level that can be processed by the control circuit of the PC.

FIG. 2 shows the configuration of a conventional input circuit. In the figure, for example, when an input signal 5i21 of DC 12V is input to the input circuit 21, it passes through the resistor R20 to the photocoupler PH21.
Current flows through the diode of , which turns on the transistor and generates the signal 5o21, which is sent to the PC (not shown).
control circuit. The resistor R30 is a resistor for bypassing the leakage current from the diode of the photocoupler PH21 when the switch on the input side is turned off.

The input circuits 22 and 2n have a similar configuration, and generate signals 5o22 and 5o2n when input signals 5i22 and -3 i 2 n are input, respectively. Normally, these input circuits are configured as an input module 200 by collecting, for example, 16 circuits into one.

On the other hand, the voltage of the signal generated on the machine side is 2V in addition to 12V.
There are 4V, 48V, etc. If you try to cover all voltages in this range, heat generation from each resistor (heat generation is proportional to the square of the input terminal ratio) becomes a problem, and the photocoupler transistor must be turned on reliably over a wide range of input voltage fluctuations. In reality, input modules are prepared for each type of voltage because it is difficult to determine the circuit constant for turning off the switch.

[Problem to be solved by the invention]

However, it is complicated to select input modules one by one depending on the input terminal. Furthermore, in systems where multiple types of input voltages exist, it may be necessary to use input modules with other input terminals instead of using all the input circuits in one input module, which is uneconomical. .

The present invention has been made in view of these points, and it is an object of the present invention to provide an input circuit for a programmable controller that can easily cope with changes in input voltage.

[Means to solve the problem]

In order to solve the above problems, the present invention provides an input circuit for a programmable controller that receives an external input signal and converts it into a digital signal at a predetermined voltage level. There is provided an input circuit for a programmable controller characterized by comprising a constant voltage circuit that stabilizes the voltage to a constant voltage.

[Effect]

When the number of input terminals increases, the heat generated from each resistor installed on the output side of the constant voltage circuit does not increase, and the power consumption of the control transistor of the constant voltage circuit only increases in proportion to the input voltage. . Therefore, it becomes possible to share one input circuit for several types of input voltages.

Further, since the current at the time of signal input is constant, it becomes easy to determine circuit constants.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a circuit diagram of an input circuit of a PC according to the present invention. In the figure, the input signal Sil of the DC voltage Vi is the constant voltage circuit 1
0, is applied to the diode of photocoupler PH1 through resistor R2. The resistor R3 is connected to the photocoupler PH1 by the leakage current when the switch on the input side (not shown) is turned off.
This is a bypass resistor to prevent the transistor from turning on.

In the constant voltage circuit 10, the transistor Q has an emitter
It operates as a follower amplifier, and its base is driven by the potential at the connection point of the series circuit of resistor R1 and Zener diode Z, and the output side is V, = V2 - V, E
(1) However, V2: Zener voltage VB of Zener diode Z: A constant voltage V of the base-emitter voltage of transistor Q appears. For example, 7V is used as the Zener voltage V2, and when the input terminal Vi is higher than the Zener voltage V2, the Zener diode Z maintains the Zener voltage V2, and the collector current of the transistor Q increases or decreases in response to load fluctuations. , the voltage V is a constant value defined by the base potential of the transistor Q. The upper limit of the input terminal Vi is determined by the capacitance of each element, but here it is configured to cover at least 48V.

Here, Vs = lL3 + IpH) R2 + Vp, i (2) However, I,3: Current I flowing through resistor R3 PH: Current flowing through the diode of photocoupler PH VPH: Forward voltage drop of diode of photocoupler PH (approximately 2V ) Therefore, from equation (2), the current I PH is calculated by the following equation I PH -
(Vs Vpo)/R2Vp□/R3° (3) It becomes a constant value.

Also, the current r R1 flowing through the resistor R1 is IRI<IE'
H, and the input current Ii can also be considered to be approximately constant regardless of changes in the input terminal Vi. In this way, since the current IPH and the input current Ii are constant when a signal is input, the circuit constant for turning on the transistor of the photocoupler PH1 can be easily determined. In addition, the transistor Q
Since the collector current is constant, the power consumed by the converter increases or decreases in proportion to the input voltage.

Next, when the input voltage Vi is smaller than the Zener voltage V2, the current IPH is IPH= (VI VILE Vpo) / (
R1/br@10R2)-V,/R3'' (4) From this equation, the off-state conditions can be found.

As described above, in the input circuit 10, 12V to 4V
It is possible to receive an input signal with a voltage in the range of 8V, which is converted into a 5V digital signal S01 and transmitted to a control circuit (not shown).

The human power module 100 houses, for example, 16 input circuits having the same configuration as the input circuit 1 described above. Then, each input circuit receives the input signals Si1 and 5i16 manually, thereby generating digital signals Sol and 5i16 respectively.
5o16 is generated and transmitted to the control circuit.

Note that although the case of a DC input signal has been described above, in the case of an AC signal, a wide range of voltages can be easily handled in the same way by providing a rectifier circuit at the front stage of the constant voltage circuit.

〔Effect of the invention〕

As described above, in the present invention, since a constant voltage circuit is provided to stabilize the input signal voltage to a constant voltage, there is no need to select a manual module depending on the input terminal, and the system design is simplified. In addition, since input signals of various voltages can be received by one human-powered module, the utilization rate of the input module can be increased and economical efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an input circuit of a PC according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional PC input circuit. 0 00 Sil~5i16 So1~S016 ■! input circuit ・° Constant voltage circuit input module input signal output signal input voltage Figure 1

Claims (2)

[Claims] (1) In the input circuit of a programmable controller that receives an external input signal and converts it into a digital signal of a predetermined voltage level, the input signal voltage in a range of at least four times the specified voltage is stabilized to a constant voltage. An input circuit for a programmable controller characterized by comprising a constant voltage circuit. (2) The input circuit for a programmable controller according to claim 1, wherein the specified voltage is 12V.