JPS5940484A - Electric heater of temperature controllable plural systems - 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 The present invention relates to controlling the temperature of an object heated and kept warm by two or more electric heaters having different thermal properties.

As an example of an object to be heated and kept warm, consider a pipeline that transports heavy fuel oil that is heated and kept warm by electric heating.

The input control of electric heaters in this pipeline can be roughly divided into a)
At the time of pipeline startup, that is, control to heat up from room temperature to a predetermined temperature in a predetermined time, b) To maintain the pipeline temperature steadily at a predetermined value, control of heat loss due to changes in external conditions such as air temperature. It is possible to think of a control system that responds to fluctuations. These controls can be controlled by adjusting the heating power supply voltage, but here we will consider the simplest on/off control.

The above input control is simple when there is only one pipeline and the thermal characteristics are constant along its length, but 1) when there is only one pipeline but the thermal characteristics are not constant along its length, 2) ) When there are multiple pipelines and each pipeline has different thermal characteristics, it is necessary to treat the parts with the same thermal characteristics as one system and perform independent input control for each system, resulting in high equipment costs. become.

One way to avoid this increase in equipment costs is to install a temperature sensor (detector) in only one system, preferably one with a heat-saving time constant, and control all systems at once (see the following literature: 4?Permission announcement 18427-1989 (Patent No. 628
, No. 152) “Temperature control method for heating pipeline”)
Methods such as these are being used. However, with this method, it is generally impossible to simultaneously satisfy the above-mentioned controls a) and b).

The present invention aims to solve this difficulty.

Now, before explaining the present invention, in order to give a more general explanation, the symbol is Qn (Kcal/1n-hr) 1 [1st time of the nth electrically heated body (for example, a pipeline). , input per length (heat generation of heating element) q n (Kcal 7kn -hr) Similarly, heat loss αn at a given heating temperature (Kca17fn-hr-℃) Similarly, loss coefficient (
Congratulations on the heating element. ) 1 n (Kcal/m-℃) Also high fever (same as above.) T
n (br) Similarly, thermal time constant (same as above) (Tn =
rn7ttn) Qn (℃,) Same〈Temperature θ, (℃) Predetermined heating temperature of the heated object t (llr) Time after heating start n (-) Number of systems and 1 To simplify the problem, t = o In this case, the temperature of the electrically heated body is 0°C, and the ambient temperature is always 0°C. Then, Qn becomes K as follows.

Now, in a strain of n=1.2, always T, <T! +2), and Q represents on when t = , -s.
For n7αn, if we consider the case when α direct α2, the time course of θl and θ! will be as shown in Figure 1a. In Figure i1a, θ electric.

The solid line portion of θ2 indicates that heating is being performed continuously,
This shows that the time from the start of heating until the θ temperature reaches the predetermined temperature is tsl.

After this time tsI, generally Qn ) /1. n==αnθ, (4). In other words, the system of 2L=1 (system of θ1) is Q+>〆1=α1θ□
(5) Therefore, it becomes necessary to turn the power on and off in order to match the input by Q with l.

Then, since it is assumed that the two systems 11=1 and 2 are connected to the same power supply, the system n=2 (system θ2) is turned on and off at the same time even though it has not yet reached the predetermined temperature or. In FIG. 1a, the temperature θ1 of the part that is turned on and off. θ2 is shown as a broken line to indicate the average temperature. In other words, this part as well) 1. , has a minute temperature range Δθ depending on whether it is on or off.

Now, as mentioned above, at tsl, θ2 still reaches the predetermined temperature [(-) Since the human power is limited, the time ts2 to reach 01 may exceed the time to be reached.

One way to avoid this is to replace equation (3) by making ts2 coincide with a predetermined time, but then as shown in Figure 1b, t > ts2 and 0.
2〉θ and (the force θ, exceeds the temperature limit of the heated object and is sometimes dangerous.

In order to avoid this danger, Q, /
As α1=(↓ri/α2, M lc is 1 as shown in the diagram.
During S de + t S 2, the system with n = 2 is n =
Unlike system 1, if it can be made to turn on instead of turning off (the time for θ! to reach 01· in this case is ts≦), compared to ts2 in the case of Figure 1a, Therefore, ts; can be reduced to ts2<ts* (8).

On the other hand, even in the case of equation (6), θ is the predetermined value θ.

After reaching , there is no danger of equation (7) if it is possible to restrict the input to the second system compared to the first system, as shown in equation 01 below.

In the present invention, after the temperature of one system (the first system in FIG. 2) of the plurality of systems of heated objects heated by the plurality of systems of heating elements supplied with power from the same power source reaches a predetermined temperature θ1, Even when input ON/OFF commands are issued to the heating elements of the plurality of systems, it is ensured that the situation shown in t) tg, shown schematically in the fiib diagram, does not occur as shown in equation 7), and as shown schematically in Fig. 1c. Thus, between tsI and ts2, that is, until the θ earthquake reaches a predetermined temperature or, the second system L is turned on, or even if it is turned off, it remains turned on for a long time, or both. I'm trying to make it work.

The present invention provides one system of heating elements (9°14,/6) (hereinafter referred to as A temperature detector (4) and a temperature detector (4) connected to one of the plurality of systems of heated objects (the temperature similar device, if any) (1) are installed. In a multi-system electric heating device capable of controlling temperature by installing a temperature control device @ for monitoring, a load switch (7 , 12, 16) (hereinafter sometimes referred to as a switch) is installed V1, the temperature control device and each load switch are connected by signal wiring m01, and the signal wiring is in progress corresponding to each load switch. Equipped with a timer! (6, tl, 1s) is inserted.

Let's explain this using Figure 2.

In Fig. 2, unlike Fig. 1, the object to be heated is 1.
2.3, respectively, electric heater 9.14.18
is heated. It is preferable that the thermal time constant T1 of the heated object 1, which also serves as a monitor, be smaller than either of the other heated objects 2 and 3, or close to the smaller of the two. Temperature detection (sensor) 4 is object 1
The signal is transmitted to the temperature controller 22 through the wiring 5.

(-L, the on/off signal from the controller 22 is wired 10
Switch (usually magnetic switch) for input control to heater 9.14.18 by 7°12.16,
Timer C time limit) is communicated via device 6, 11.15.

The roles of the timer devices 6, 11, and 15 are as follows.

First, considering the start of heating, the timer device 6 keeps the input to the heater 9 on until the time ts1 when the temperature of the heated object 1 reaches a predetermined value θr shown in FIG. 1a, and after the temperature reaches the predetermined value. is turned on and off so that "average value of θ1=or". However, heated object 2. Regarding B, if the time constant is 'L (T*, 'L (9)), θ2 and θ3 have not yet reached Or.

Therefore, the role of the timer device 11 of the second system in FIG. At t4tt, the switch 12 remains on or remains on for a relatively long time.

The same thing can be done in the sixth system by using the timer device 15. After reaching a steady state through these steps, the action of the timer device described below or i13
After tS2 in the figure, batch ant control may be performed as in the case of IC.

Next, the roles of the timer devices (5, 11, 15, etc.) in the steady state after all systems reach the predetermined temperature θr will be explained.

Now, the average temperature of the heated object in the first system in a steady state is θlr + that of the second system is θ2r, and the switch-on (closed circuit) time of the first system is t7. 11□ that of the second system
Then, these and Qv'ct +.

Between Q and /α2, ty <<'r l + t 1
2 <<Tt & C The following equation holds. Therefore, it is sufficient for θl,=O,r. However, since the equation (1) only gives 112/j7, the absolute values of tt and tIx can be arbitrarily selected by adding up the equation (11).However, if you choose t1+tll which is too large, In figure 1C, θI and θ
.

Even if the average value (θ, 0−r) is constant and equal, it cannot be denied that the slight temperature width Δθ (Δθ1.Δ02) becomes large.

However, when θIr=θ2r, equation (11) is obtained, and 17.1. The selection of □ is not affected by the ambient temperature e51a.

The switch opening time changes depending on the fluctuations in t and the period 1ffiFIIIθa. For example, for θpo=θ2r, θ
If a gets closer, that is, if θ3 becomes higher, the opening time of switch 7, 12, 16 becomes longer, and if θa becomes lower, the opening time becomes shorter, but the closing time (tt e of equation 00
There is no change in tu).

That is, as the open circuit time changes, the ratio of the closed circuit (heating) time to the open circuit time changes, and input adjustment per unit time is performed to accommodate fluctuations in θa.

From what has been said above, in FIG. 2, the temperature of the heated object 1 with the sensor 4 decreases and the temperature is adjusted? When the signal from the p-meter 22 is transmitted to the timer device 6.11 and commands the switches 7 and 12 to close, the timer device 6.1
1, the closing time t7+tl of switch 7.12 is set to satisfy the relationship of formula 00! is realized, and the average temperatures θ of the heated objects 1 and 2 become approximately equal.

Generally, in the case of pipeline heating, T,,T.

Etc. ranges from several hours to tens of hours, and '? Since + is within a few minutes to more than 10 minutes, the above [9J section is usually established with sufficient accuracy. Usually ty/T+ or t,,/T! If it is 1/10 or less, it is practical.

Next, when the circuit closing time '7+tH etc. has elapsed, the heated object 1,
The temperature of 2 is a minute temperature range △θhΔ from the moment the switch is turned on.
It has risen by θ2, and swing-f-7 and f-12 are opened by the command from the timer devices 6 and 11. Then, the temperature of the heated objects 1 and 2 begins to drop, and when ΔO9 and Δθ2 drop, a signal from the temperature controller 22 connected to the sensor 4 reaches the timer device 6.11, which instructs the switch 7°12 to close. . These operations are repeated as long as the temperature of the heated object remains in a steady state.

The control at the time of start-up before the control during the steady state may utilize the action of the timer device described above, but it is also possible to use the control at the time of startup before the control during the steady state. You can control it.

As described above, the present invention is characterized in that in a steady state, the temperature controller 22 issues only a command to close the heating circuit, and opens the circuit U: by a command from the timer device, and tljl'7 is expressed by the relationship of equation 01). If set, the two systems will be kept at the same average temperature regardless of the ambient temperature θa. This means that the system is 6':), and as mentioned above, the timer device is activated at ts
＋l'S! It must be possible to set one or two fills such as tll + 17 during normal operation and steady state.

Now, there is a method as in the present invention in which only one system of heated objects is used as a monitor for temperature control, and a timer device is used to heat and keep the heated objects together with other heated objects, and a known method has independent temperature controllers for each of the heated objects. Let's explain the economic comparison using Figure 2.

In Figure 2, A indicates the object to be placed in the central control room, C indicates the heated object placed at the plant site, and B indicates the connection wiring 5, 8, 13, 17 between A and C. A(!:
If C is very close, known methods may be economical. However, if C exists over a wide area such as in a pipeline, and therefore B is a long distance, the method of the present invention is better than the known method, which requires a sensor 4 and a wiring 5 for each object to be heated. Since these can be omitted, it is economical.

Furthermore, providing the sensor 4 is a weak point in the heating and heat-retaining vibrator line. Particularly when the pipeline is outdoors, special attention to waterproofing etc. is required, so the advantage of having the sensor 4 at only one location as in the method of the present invention is significant.

In the above, a sensor was installed in one system of the heated object, and this was used as a monitor to control the temperature of all systems.
It is also possible to provide a separate temperature simulator (simulator) in place of the object 10 and use it as a monitor, as in the case of Japanese Patent Publication No. 18427/1986, written in IIJ, and this is another aspect of the present invention. It is.

The meaning of using the system with the smallest or closest time constant as a monitor among the systems of the heated object is as follows:
This means that the aforementioned minute temperature width Δθ (ΔθI, Δθ2) can be made as small as possible. However, as long as the ΔO of all systems is within the permissible range, any system can be used as a monitor.

[Brief explanation of the drawing]

1a to 10 are for explaining the operation of the method of the present invention.
Diagram showing the relationship between time, input, and temperature rise for the two systems under three different conditions. Figure 2 is a schematic diagram showing the control connection system when there are three heated objects, 1, 2.3 are three heated objects, 4
1.5 is the connection wiring between 22 and 4; 9.14.18 is the heating element; 7,
12.16 is a switch to turn on/off these heaters, 8.1ro, 17 is the connection wiring between those heaters and the switch. 6.11.15 is a timer device, wiring connecting the 1011-1 temperature controller 22 and these timer devices, 19 is a power source, 20 is a power switch, and 21 is a power supply line. Below 1-Ma1c ward descend, to season 1≦%2fη=2.
．． Go to 6

Claims (2)

[Claims] (1) One system of heating elements (9, 14° and 8) that is supplied with power from the same power source is provided to each of the plural systems of heated objects (one of which may be a temperature similar device), A temperature detector (
4) and the temperature control device c! connected to this! In an electric heating device with multiple systems capable of temperature control with a monitor installed, a power supply line (8, 1:
! 1, 17), each load switch (7, 12, 1
6), connect the temperature control device and each of the load switches with a signal wiring Q (+1), and install a timer device (6, it, 15') in the signal wiring corresponding to each load switch. ) is inserted into the electric heating device. (2) Clause (1) characterized in that the heated object of system - which is used as the monitor has the smallest thermal time constant or one that is close to this among the heated objects of all systems. Electric heating device as described.