JPS6285629A - Instrument disconnection detecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention uses an alarm setting device, which is a secondary instrument, to detect an abnormal decrease in the state quantity of a process in the auxiliary equipment control of a switchboard, and uses this contact output to trip the auxiliary equipment. This invention relates to a disconnection detection circuit for an instrument circuit for detecting disconnection on the instrument side and preventing erroneous output when configuring the circuit.

[Background of the invention]

Methods for detecting process state quantities (temperature, level, pressure, etc.) and extracting them as contact outputs are as follows: 1) Method using mechanical instruments (e.g. temperature → bimetal switch, level → float switch, etc.) 2) Process quantity as primary Instruments (e.g.
Thermocouple or other detector) converts it into an electrical signal,
A method of outputting contact information using a secondary meter such as an alarm setting device.

There are 2 types, and each of these is used depending on the process state quantity, etc. Especially when using method 2) above,
If you use an alarm setting device that allows you to arbitrarily set lower and upper limits for contact output, but if you use the 5 output contacts not for alarms but for interlock circuits such as trip circuits,
Care must be taken to ensure that contacts do not malfunction and auxiliary equipment does not trip in the event of an abnormality in the instrument circuit power supply or disconnection of the instrument circuit.

As an alarm setting device used in general instrumentation circuits, it has the function of excitation during normal conditions and excitation during abnormal conditions.Measures against instrument power supply abnormalities can be made by selecting the appropriate excitation force type according to the application. However, when it comes to wire breaks, the setting device itself usually does not have a wire breakage detection circuit (it is originally intended for alarm output, so there is no function to lock the output in the event of a wire break). An example in which the output of the alarm setting device malfunctions when a meter circuit is disconnected will be explained with reference to the alarm setting device operation diagram shown in FIG. 2. This figure is an example of the case where the lower limit setting output is used, and the process amount is detected by the primary instrument,
When this electric signal quantity a is input into the setting device, a negative signal conversion is performed.

This is added to the setting signal b (positive signal) of the setting device, and this deviation signal C becomes positive when the relationship a < b, that is, the process amount becomes smaller than the setting, and is amplified by the amplifier d and internally Relay: Energize e, lower limit output contact:
Output f to the outside. In this case, if a disconnection accident occurs between the primary meter and the alarm setting device, the signal: a is cut off, and the setting signal = b inside the setting device is output as is as the deviation signal: C.

The internal relay will malfunction. In the case of upper limit setting, the internal circuit is exactly the same except that the signs of the output signal a of the primary meter and the setting signal b in FIG. 2 are reversed. In other words, in the case of the above disconnection accident, the input signal: a
is cut off, but since the internal setting signal is negative, the internal relay is not energized.

From the above, when setting the first signal setting device to the lower limit and configuring the trip circuit of the auxiliary equipment with its output contact, it is necessary to detect the disconnection and lock the trip circuit. An example of a conventional circuit including this countermeasure is shown in Figure 3. This circuit detects that the temperature has dropped due to some kind of abnormality after the steam temperature has reached a specified temperature under steady-state operation, and trips the related auxiliary equipment. By connecting the contacts in series, it is possible to prevent malfunctions in the event of a disconnection. The circuit is a thermocouple for temperature detection as an instrument circuit: TH-1゜TH-2, an alarm setting device: AM-1, AM-2, a timer for monitoring the instrument power supply:
It is composed of a TR, auxiliary relays: AD as a trip circuit, and timers T1 to T4. The output of the alarm setting device is a contact that closes at the specified temperature (upper limit setting) in steady operating conditions:
x' and Y' are contacts that close at the trip set temperature (lower limit setting) = X' and Y', and these are used to prevent malfunctions when the instrument power is turned off and restored, when the instrument power becomes normal and a few seconds have passed. The contacts are amplified by the auxiliary relays A to C based on the AND condition with the timer contact TR' which closes later.

Now, when the system is in steady operation and the steam temperature reaches the specified value, contacts X' and Y' close, energize the auxiliary relay A, whose contact A' closes, and energize the auxiliary relay D. , is self-held by its contact point =D'. After that, when the appropriate temperature for the trip setting drops due to a system abnormality, the contacts = X' and Y' open, and the contacts x' and Y' close, and the respective auxiliary relays;
Excite B and C and their contact point: B'.

C' closes and energizes timers Tl and T2 through the contacts. Timer 2 T2 (after 2 seconds to prevent malfunction)
The output of the related auxiliary equipment becomes the trip output, and when the timer setting time reaches the setting time of the timer: T1 in the relationship T2 (T), the contact: T r ' opens, and the auxiliary relay =
When D is de-energized and contact D' is opened, timers TI and T2 are also de-energized, and the temperature drop detection circuit is returned to its pre-operation state.

Here - after reaching the specified temperature (D is in the excited state) AM -
If a disconnection accident occurs between T H-1 + A M-1 in the 1-side instrument circuit, the output contact of AM-L = x' will open and X' will close according to the above explanation, but AM -2
If the side instrument circuit is healthy, the output of AM-2 is Y' is closed,
Y' is in the open state, auxiliary relays A and C are not energized and only B is energized, and trip output timer 2 T is in the open state.
1 and T2 are never energized. However, contact point = B'
is closed and C' is open, so timers T8 and T4 are excited, and the output of timer T3 is output as an alarm to the outside as a detector abnormality. (The setting of timer T3 takes into consideration the difference in operating time of AM-1 and AM-2 during normal operation, and the setting time is several seconds.) After that, the setting time of timer = T number (T a < T 4 ), the contact point: T4'
is opened and the detection circuit is reset. After a detector abnormality alarm is output, the automatic trip circuit will be locked until the cause of the abnormality is corrected.

This will lead to a transition to monitoring and control by operators using recording meters or indicating instruments.

In this method of duplicating instrument circuits such as 7-alarm setting devices, as the number of component devices such as alarm setting devices increases, a primary instrument (thermo couple in this example) is also added, so additional system piping work is required. Also, if a disconnection accident occurs when two lines are connected (the probability of this happening is extremely small, excluding panel fires, etc.).

There was a problem in which an alarm was not output for a detector abnormality even though a mistrip occurred.

As a conventionally known example of wire breakage detection, there is a "remote detection method for cable breakage" that requires manual operation (Japanese Patent Application 1973-
89797) etc.6 [Object of the Invention] An object of the present invention is to provide a disconnection detection circuit for an instrument circuit that reduces the number of components and reduces the cost.

[Summary of the invention]

The instrument circuit, including the alarm setting device, is configured with only one system without duplication or tripling, and disconnection of the input signal line to the alarm setting device is detected by the alarm setting device, which changes instantly when the line is disconnected. The contact operation can be extracted and detected using a timer and auxiliary relay.

[Embodiments of the invention]

An embodiment of the invention is shown in FIG. It is composed of a thermocouple: TH-1 as an instrument circuit, an alarm setting device: AM-1, a timer for monitoring instrument power supply: TR, an auxiliary relay: AD as a trip circuit, and timers T1 to T4. AM-
Output contact 1 is a contact that closes at a specified temperature in steady operation (
Upper limit setting) = X' and contact that closes below the trip set temperature (lower limit setting) = x', timer contact for instrument power supply normality confirmation: TR' and auxiliary relay under AND condition:
Contact points are amplified by A and B. The circuit operation for detecting a temperature drop is basically the same as the conventional circuit shown in FIG. That is, when a steady operating state is reached and the specified temperature is reached, the contact x' closes, energizes A, and closes the contact A', thereby energizing D and self-holding by the contact D:. If the temperature drops due to a system abnormality in this state, when the temperature drops below the specified temperature, contact x' will open, A will be de-energized, and b contact A' will close, and timer T3 will be energized for the set time. If it is set for a short time of 1 second, the timer 2 T will continue until the temperature further drops to the trip setting temperature (contact B' is closed).
Contact a has already reached the set time.

Ta' is open, and auxiliary relay C and timer T4 are not energized. After that, the temperature drops to the trip setting temperature, contact x# closes, energizes B, and contacts 2B'
When closed, timers T1 and T2 are energized through contacts D' and C', and a trip output is generated. Timer:
The detection circuit is reset when the set value of T1 is reached, as in the case of FIG. 2.

In addition, after reaching the specified temperature, the instrument circuit TH-1)
-) If a disconnection accident occurs between AM-1, the contact of the alarm setting device will instantly change from closing to opening.

X" opens and closes, so if the contact operation is within the set time (1 second) of timer T8, the auxiliary relay C and timer hinge are energized simultaneously through contacts T3' and B'. Contact: C' opens and trip circuit (timer 2 Tl and 12
circuits). Furthermore, the output of contact 20' alerts the outside of the detector abnormality. After that, when the set time of timer 2 T4 is reached, contact No. T opens, auxiliary relay D is de-energized, contact D' opens, and since contact A' is already open, the main detection circuit is restored. However, the trip circuit is never energized.

As described above, according to this method, it is possible to effectively detect a disconnection with only one alarm setting device without requiring the addition of any component equipment such as a primary detector or the expansion of system piping.

〔Effect of the invention〕

According to the present invention, it is possible to reduce the number of connection cables between the field and the control panel, and the number of wiring steps within the control panel.Furthermore, there is no need for additional system piping work, and the number of component devices can be reduced, thereby improving the product quality of the panel. can be achieved.

[Brief explanation of drawings]

Fig. 1 shows an implementation circuit of the present invention, Fig. 2 shows an explanation diagram of the operation of the alarm setting device, and Fig. 3 shows a conventional circuit. TH-1...Temperature detector (thermo couple), AM-
1...Alarm setting device, A-D...Auxiliary relay, Tz~
Ta, TR...timer.

Claims (1)

[Claims] 1. Primary meter (electrical signal conversion) detects an abnormal drop in process state quantities (temperature, level, etc.) in the control of auxiliary equipment on the switchboard
If the alarm setting device (contact output conversion), which is a secondary instrument, is used to configure a trip circuit for an auxiliary device, the alarm setting device may malfunction due to a disconnection between the primary instrument and the secondary instrument.
A circuit characterized in that, in order to prevent auxiliary equipment from mistripping, a timer and an auxiliary relay detect instantaneous contact operation at the time of disconnection, and detect disconnection in the meter circuit.