JPS6044686B2 - Line heater control method - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in line heater control methods.

Conventionally, piping systems have been used to store gas fluids that solidify when cooled.

(hereinafter referred to as "line"), the process of distributing
A heater is wound around the line and the power is turned on and off to ensure smooth fluid flow. Therefore, the line of the process is more than conventional.

The one-step control system uses a comparison circuit that compares the upper limit temperature set value and lower limit temperature set value with the actual line temperature, and a comparison circuit that is connected to the output side of this circuit to order the temperature rise process in consideration of the temperature characteristics of the fluid. The heater is equipped with a power control circuit that outputs a power off signal with hysteresis or reverse hysteresis of the temperature decreasing process, and the heater power is turned on and off using the on/off signal of this power control circuit. To explain this with reference to Figure 1, power supply control using forward hysteresis is performed when the line temperature reaches the upper limit temperature set value TH (see Figure 1).
, the power supply control circuit outputs an OFF signal and the heater power is cut off, and when the line temperature drops and reaches the lower limit temperature set value Tl, the power supply control circuit outputs an ON signal and the heater power is cut off, as shown in the figure. The heater power is turned on and controlled.

As shown in FIG. 3c, the power supply control based on reverse hysteresis is such that the heater power is turned off at the lower temperature set value Tl and turned on at the upper temperature set value TH. However, the line heater control method described above uses forward or reverse hysteresis and controls the power on and off using the upper temperature set value and lower temperature set value, so temperature followability is poor and the process In some cases, the delay in heat transfer is not clear, or it is difficult to determine whether to use forward or reverse hysteresis to control the heat transfer because the heat transfer is directly affected by the ambient temperature.

The present invention has been made in view of the above-mentioned circumstances, and is capable of controlling the power supply of forward hysteresis and reverse hysteresis by controlling the heater power supply on/off by taking into account the temperature gradient as well as the upper and lower limit temperature set values. The purpose of the present invention is to provide a line heater control method that has excellent ability to follow disturbances such as environmental changes and can realize smooth control that matches the characteristics of the process target without constructing a circuit. An embodiment of the present invention will be described below with reference to FIG.

In the same figure, 10 and 11 are heat capacity setting devices for the line itself and the heat insulating material, and the respective heat capacity setting values are set to A (ca
1rC-rrL. ), B (ca11℃・rri.). In addition, 12 and 13 are heat capacity setting devices that emit heat from the heater and line to the outside, and set the respective heat capacity settings as C (ca1rC-m) and D (Ca1rC-TTI,).
shall be. 14 is the heat capacity setting value A. of the line and insulation material. ．． B
15 is a subtraction circuit that subtracts the external release heat capacity set value D from the heat capacity set value C of the heater.

This C. , D is the heat loss
This is the heat capacity setting value that determines the C-D support. What about 16? of
A division circuit that calculates the set value temperature gradient M during line heating by performing A + B calculation, 17 performs the calculation of 1゜
A + B is a division calculation to find the set value temperature gradient N when the line is not heated.

18 is a subtraction circuit that subtracts the heating temperature gradient M from the actual line-measured temperature gradient S, and 19 is a subtraction circuit that subtracts the non-heating temperature gradient N from the actual line-measured temperature gradient S.

Reference numerals 20 and 21 indicate an upper temperature setter and a lower temperature setter for setting an upper limit temperature set value TH and a lower limit temperature set value TL in accordance with disturbance resistance, process characteristics, etc., and these set values 20
, 21 set values TH, , TL are set by the comparator circuit 22, respectively.
, 23, the temperature is compared with the line-measured temperature T.

24 and 25 are OR circuits, and 26 is a hold circuit.

Next, the operation of the line heater control method configured as above will be explained. As shown in FIG. 3, when the temperature a at the time of suit start is lower than the lower limit temperature set value TL, the measured temperature a and the lower limit temperature set value TL1 of the lower limit and upper limit temperature setting devices 20 and 21 are set as the upper limit temperature set value TH. Comparisons are made by comparison circuits 22 and 23, respectively. As a result, an off signal is output from the comparator circuit 22 and an on signal is output from the comparator circuit 23.
The signal enters the hold circuit 26 via the R circuit 25, where the heater power ON signal is held and the heater power is turned on. At this point, the line temperature gradient S does not have a slope yet, so an off signal is output from each of the subtraction circuits 18 and 19. When the heater power is turned on, the line temperature gradually rises, and the dividing circuit 16 obtains a temperature gradient M during heating, which is input to the subtracting circuit 18.

At this time, the other input section of the subtraction circuit 18 contains the actual line-measured temperature gradient S. Therefore, in this subtraction circuit 18, both temperature gradients M. ．． When the relationship S/) Mamoru = s>M is reached, an ON signal is output from the same circuit 18, which is OR.
The signal enters the halt circuit 26 via the circuit 24, and the circuit 26 is reset. As a result, the hold circuit 26 releases the hold state and the heater power is immediately cut off. When the heater power is turned off, the residual heat continues to rise for a certain period of time, but after that it shifts to a falling state.

And this downward slope is a constant condition, that is ■! When =s<N, an ON signal is output from the subtraction circuit 19, and this is the OR signal.
It enters the hold circuit 26 via the circuit 25. As a result, the circuit 26 holds the on state and turns on the heater power again with this on signal. Therefore, with this control method, it is possible to always control the heater power on and off between the falling temperature set value TL and the upper limit temperature set value L, and in turn, it is possible to quickly follow the temperature within a certain temperature range and control the line. Temperature control can be performed.

Next, after the initial power supply to the heater is turned on, the temperature continues to rise as shown by the dotted line (A) without the temperature gradient condition being met.
When the line temperature exceeds the upper limit temperature setting value TH, an on signal is generated from the comparator circuit 22 and enters the hold circuit 26 via the OR circuit 24.

Therefore, the hold circuit 26 releases the on state and immediately cuts off the heater power. However, in reality, the condition due to the temperature gradient is satisfied before the line temperature reaches the upper limit temperature set value TH, so the line temperature does not change with a large amplitude but changes along the temperature curve shown by the solid line in Figure 3. . Therefore, it is not necessary to combine a forward hysteresis circuit and a reverse hysteresis circuit as a power supply control circuit, and to select and use them in consideration of the influence of heat transfer due to ambient temperature. As described in detail above, according to the present invention, in addition to controlling the heater power supply on/off by determining the lower limit temperature and upper limit temperature, the temperature gradient due to the line, heat insulating material, etc. and the actual line measurement temperature gradient Since the heater power supply is controlled to be turned on and off when certain conditions are met based on the relationship between The heat capacity and the heat capacity released to the outside are set, and the set value is calculated based on this, and it follows disturbances such as environmental changes and performs fine control that matches the characteristics of the process target (line, etc.). be able to.

Furthermore, since the heater power is turned on and off depending on the temperature gradient condition being met before the lower limit temperature set value and upper limit temperature set value are reached, line temperature control is possible with no wasted time and quick follow-up performance. This allows good control of the line temperature.

[Brief explanation of the drawing]

1a-c are temperature curve diagrams and heater power supply on/off control diagrams for explaining the conventional line heater control method; FIG. 2 is a block diagram of a device to which the line heater control method according to the present invention is applied; The figure is a diagram illustrating the operation of the apparatus according to the present invention. 10...Heat capacity setting device for the line itself, 11...
Insulating material heat capacity setting device, 12... Heater heat capacity setting device, 13... Line external release heat capacity setting device,
14... Addition circuit, 15... Subtraction circuit, 16, 17... Division circuit, S...
Line measurement temperature gradient, 18, 19... Subtraction circuit, T... Line measurement temperature, 20...
Upper limit temperature setter, 21...lower limit temperature setter, 22,
23... Comparison circuit, 24, 25... OR circuit, 2
6...Hold circuit.

Claims (1)

[Claims] 1. Means for determining the temperature gradient during heater heating and non-heating from the heat capacity set value and external release heat capacity set value of line elements such as lines, insulation materials, heaters, etc., and the temperature of line elements during heating and non-heating using this means. a two-system first comparison circuit system that compares the gradient with an actual line-measured temperature gradient of the line element; and a first comparison circuit system that compares an upper limit temperature set value and a lower limit temperature set value with the actual line-measured temperature of the line element; 2
Hold the ON signals of the second comparison circuit system of the system and the first and second comparison circuit systems belonging to the non-heating system, and hold the ON signals of the first and second comparison circuit systems belonging to the heating system. A line heater control method comprising: a hold circuit whose state is released; and an output signal from the hold circuit controls power supply to the line heater.