JPH0283465A - Method for detecting disconnection - Google Patents

Abstract

PURPOSE:To provide a disconnection detector of a high speed even when an input filter is made large by adding a photocoupler and a pulse transformer to the pre-stage of the input filter of an analogue input apparatus. CONSTITUTION:The signal of a thermocouple 11 is amplified by a differential amplifier 14 through a filter consisting of a resistor 12 and a condenser 13. An assembly wherein the secondary winding of a pulse transformer 25 and the primary winding of a photocoupler are connected in series is connected to the predetermined stage of the filter and a pulse is supplied to the primary side of the pulse transformer 25 through a driver 26 and the output on the secondary side of the photocoupler 22 is supplied to an FF 24. When the thermocouple 11 is not disconnected, a pulse current I2 flows through the thermocouple 11 and, therefore, the output of the photocoupler 22 becomes large but, when the thermocouple 11 is disconnected, only a pulse current I2 flows and the output of the photocoupler 22 becomes small to make it possible to detect disconnection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low voltage input analog input device, and particularly to a disconnection detection method suitable for increasing the speed of disconnection detection.

[Conventional technology]

As described in Japanese Patent Application Laid-Open No. 49-32024, the conventional device takes in analog input signals from multiple points in one time division, applies a voltage for detecting disconnection for a certain period of time for each input process, and
When the input signal line is disconnected, this method performs disconnection detection on the condition that the amplifier output exceeds a certain voltage. Also, generally, a voltage is always applied to the input via a high resistance.
This method detects a disconnection on the condition that the amplifier output exceeds a certain voltage when the input signal line is disconnected.

[Problem to be solved by the invention]

The above conventional technology does not take into consideration the size of the input filter time constant or the speeding up of the disconnection detection time.
Not practically suitable. Alternatively, there is a problem that the disconnection detection time is long.

An object of the present invention is to shorten the disconnection detection time without deteriorating the characteristics of the original analog input device.

[Means to solve the problem]

The above purpose is to
The signal line disconnection detection method is achieved by adding a photocoupler, a pulse transformer and a pulse transformer drive circuit as means for supplying power to the photocoupler.

[Effect]

In the disconnection detection circuit, when the input signal line is normally connected, current flows through the photodiode of the photocoupler through the signal line. Thereby, the analog input device can early know whether the input signal line is normal because the photocoupler output signal becomes valid.

〔Example〕

An embodiment of the present invention is shown in FIG.

The operation will be explained below using FIGS. 1 to 4.

In this embodiment, a thermocouple 11 and a resistor 12 configuring an input filter are used as input signals. Capacitor 13° Differential amplifier 14
．． Reverse current path diode 21, the photocoupler 22. A flip-flop 24 for storing the output of the photocoupler. Pulse transformer that supplies power 25. This is an analog input device with a disconnection detection circuit, which includes the driver 26 for driving the pulse transformer.

The input voltage range targeted by this circuit is 100 mV or less, as shown in FIG. Therefore, in normal analog signal capture operation, the diode 21 and photocoupler 2
Since the operating voltage is lower than the operating voltage of the photodiode No. 3 (see FIG. 4), the circuit including the pulse transformer 25 can operate as if it were not attached.

Next, the disconnection detection operation will be explained. When the waveform at point A in FIG. 2 is input to point A in FIG. 1, the pulse transformer 25
is excited, and currents 1 and 2 shown in FIG. 1 flow. As the current flows, the photocoupler 22 becomes O
N, and the waveform at point B in FIG. 1 becomes as shown in FIG. In this way, it can be confirmed that the input signal (thermocouple 11 in FIG. 1) line is normal.

Next, the operation when the thermocouple 11 is disconnected will be explained. When the thermocouple 11 is disconnected, as shown in FIG. 1, when the pulse transformer 25 is excited, only Iz flows through the photocoupler 22, and the waveform at point B in FIG. It will look like the broken line in Figure 2, and C
A dotted waveform indicates a disconnection condition.

According to this embodiment, there is an effect that disconnection of a signal line can be detected at high speed regardless of the time constant of the analog input circuit.

〔Effect of the invention〕

According to the present invention, in a low-voltage analog input circuit, even if the input filter is large, disconnection detection can be performed at high speed, which is effective in increasing the reliability of the system.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
3 is a diagram showing a schematic electromotive force of main thermocouples, and FIG. 4 is a schematic characteristic diagram of a diode. 11...Thermocouple, 12...Resistor (for filter), 1
3... Capacitor (for filter), 14... Differential amplifier. 21...Diode, 22...Photocoupler, 23
...Resistor (pull-up), 24...Flip-flop. 25...Pulse transformer, 26...Driver 1st
figure

Claims (2)

[Claims] 1. 1. A disconnection detection method, characterized in that, in an analog input circuit consisting of a filter circuit constituted by a resistor and a capacitor, and an amplifier, a photocoupler and a pulse transformer are added to the input stage of the filter. 2. A method for detecting disconnection, characterized in that an insulated power supply and a power supply ON/OFF circuit are added in place of the pulse transformer according to claim 1.