JPH063444Y2 - Ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to improvement of controllability of a ratio control device when a master signal is abnormal.

<Prior Art> A general configuration of a ratio control device will be described with reference to FIG.

Reference numeral 1 is a master line, for example, a raw material supply pipe in an ethylene decomposition furnace. Reference numeral 2 is a slave line, which is a steam supply pipeline controlled by a constant ratio to the raw material supply amount.

3 is a flow sensor inserted in the master line PV ₁
Is a flow rate measurement value, and 4 is a control valve also inserted in the master line.

5 is a flow rate sensor inserted in the slave line PV ₂
Is a flow rate measurement value, and 6 is a control valve also inserted in the slave line.

Reference numeral 7 denotes a master line flow controller, which operates the control valve 4 by an operation output MV ₁ obtained by control calculation of a deviation between the measured value PV ₁ and the set value SV ₁ .

Reference numeral 8 denotes a slave line flow rate controller, which operates the control valve 6 by an operation output MV ₂ which is a control calculation of a deviation between the measured value PV ₂ and the cascade setting value SV ₂ .

The ratio setter 9 uses the flow measurement value PV ₁ of the master line as a master signal and multiplies it by a constant ratio α to supply the cascade setting value SV ₂ to the controller 8.

<Problems to be solved by the invention> In such a ratio control system, when the master signal PV ₁ falls below a predetermined range due to a failure of the flow sensor of the master line, disconnection, etc., the cascade set value SV ₂
Is below the predetermined range, the supply of steam in the slave line is stopped, and the equipment of the plant may be seriously damaged.

An object of the present invention is to provide a ratio control device that solves such a problem by keeping the supply of the master signal in the normal range even when the master signal is abnormal (lower limit abnormality) in the steady state of the plant.

<Means for Solving the Problems> The structural feature of the present invention is that the lower limit of the master signal is set in a ratio control device that inputs the master signal and outputs the master signal to a ratio setter that outputs a cascade setting value. Store the set value (master signal in the measurement cycle) ≤
When (the lower limit set value), the master signal currently supplied to the ratio setter is output, and when (the master signal in the measurement period)> (the lower limit set value), the master signal in the measurement period is output. Effectiveness checking means and a change rate specified value of the master signal are stored {absolute value of difference between ((master signal currently supplied to the ratio setting device) and (output of the effectiveness checking means)} ≦ When (the change rate specified value), (the output of the validity check means) is output, and the difference between the ((master signal currently supplied to the ratio setting device) and the (output of the validity check means) is output. Absolute value >> (variation rate specified value), a rate-of-change checking means for outputting (master signal currently supplied to the rate setting device), and an output of the rate-of-change checking means are stored and held. Lies in that allowed and a master signal file as the current master signal given to the ratio setter.

<Operation> The ratio control device of the present invention monitors the master signal, and when the master signal in a certain measurement cycle falls below the lower limit setting value, or when the rate of change of the master signal exceeds the change rate specified value. Then, as this is abnormal, the master signal currently supplied to the ratio setting device is output as it is,
Keep the master signal supply in the normal range.

<Embodiment> An embodiment of the present invention will be described with reference to FIG. The same components as those described with reference to FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, signal processing is realized by a digital controller DCS having a predetermined control cycle.

The master signal PV ₁ of a certain measurement cycle is supplied to the A / D converter 1
After being digitally converted by 0, it is stored and held as M in the first master signal file 11 and supplied to the validity checking means 13 together with the lower limit set value M _L from the file 12 which stores the lower limit set value. Is checked.

When the output of the validity check means is M ′ and the master signal supplied to the current ratio setting device 9 is M ″, the determination algorithm of the validity check means 13 is M ′ = M ′ = M ′ = M _L when _M "M> M _L, 'a = M, the output M' M, the second master signal file 1
File 1 stored in memory 4 and storing the specified rate of change
Change rate check means 1 together with the change rate specified value M _K from 5
6 and the absolute value of the difference between the current master signals M ″ and M ′ is checked.

When the output of the change rate check means is M ″, the determination algorithm of the change rate check means 16 is: | M ″ −M ′ | ≦ M _K , M ″ = M ′ | M ″ −M ′ |> When M _K , M ″ = M ″, and this output M ″ is the third master signal file 17
The stored output is supplied to the ratio setter 9, and the output α · M ″ of the ratio setter is stored in the D / A converter 1.
It is converted into analog by 8 and supplied to the flow rate controller 8 of the slave line as the cascade set value SV ₂ .

FIG. 2 is a diagram for explaining the operation of the change rate check means, and the next measurement timing t due to the master signal abnormality occurring at the timing t ₂ between the timings t ₁ and t ₃ of the measurement cycle.
_{In 3} , the measured value M of the master signal has not dropped to the lower limit set value M _L, so the validity check means determines that this signal is valid.

The rate-of-change checking means monitors the difference between M ″ and M ′ at the measurement timing t ₃ , and if the difference is larger than a certain value, it is judged as abnormal.

Therefore, the device of the present invention supplies the master signal determined to be normal in the previous measurement cycle to the ratio setting device when either the abnormality detection by the validity checking device or the abnormality detection by the change rate checking device occurs. A master signal holding function is implemented. The third master signal file 17 functions as a master signal holding unit in this case.

FIG. 3 is a flow chart showing the determination algorithms of the validity check means 13 and the change rate check means 16 described above.

<Effects of Device> As described above, according to the present invention, like the ethylene decomposition furnace, when the supply of the raw material, which is the master flow rate, is cut off, the supply of the steam that is the slave is cut off. It is possible to effectively prevent the accidental damage to the inner tube, and to significantly improve the operational safety.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is an operation explanatory diagram thereof, and FIG. 3 is a flow chart diagram of a judgment algorithm of validity checking means and change rate checking means, FIG. 4 is a block diagram showing an example of a conventional technique. 1 ... Master line, 2 ... Slave line, 3, 5 ... Flow rate sensor, 4, 6 ... Control valve, 7, 8 ... Flow rate controller, 9
... Ratio setter, 10 ... A / D converter, 11, 14, 17
... First, second and third master signal files, 12 ... Lower limit setting value holding file, 13 ... Effectiveness checking means, 15
... change rate specified value holding file, 16 ... change rate check means, 18 ... D / A converter

Claims (1)

[Scope of utility model registration request] 1. A ratio control device which inputs a master signal and outputs the master signal to a ratio setter which outputs a cascade setting value, stores a lower limit setting value of the master signal (master signal in a measurement cycle) ≦ ( When the lower limit setting value) is reached, the master signal currently supplied to the ratio setter is output (master signal in the measurement cycle)>
Validity check means for outputting a master signal in this measurement cycle when (the lower limit set value), and a change rate specified value of the master signal are stored {((master signal currently supplied to the ratio setter)) And (the output of the validity check means) the absolute value of the difference} ≤ (the change rate specified value)
When (the output of the validity check means) is output, {(the master signal currently supplied to the ratio setting device)
Absolute value of the difference between and (output of the validity checking means)}>
A change rate check means for outputting (a master signal currently being supplied to the ratio setter) when (the change rate specified value), and an output of the change rate check means is stored and held as a current master signal. A ratio control device comprising a master signal file to be supplied to the ratio setting device.