JPH067891B2 - Circulation system monitoring device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an apparatus for monitoring the operating state of a plant system for circulating a chemical liquid such as a semiconductor wafer cleaning treatment liquid, and in particular, in a system using an air-driven pump as a treatment liquid conveying means, The present invention relates to a device for monitoring the operating condition.

[Technical background of the invention and its problems]

Conventionally, as a plant system that circulates a chemical liquid such as a semiconductor wafer cleaning treatment liquid, a treatment tank, a treatment liquid conveying means, and an excess means for passing the treatment liquid conveyed by the conveying means are provided. A circulation device is known in which the respective components are connected by a pipe for circulating a processing liquid.
Further, an air-driven pump such as a bellows pump or a diaphragm pump is generally used as the processing liquid transporting means of the system. In such a circulation system using an air-driven pump, it is extremely important for maintenance management to monitor the operating condition. For example, by knowing the operating speed of the pump (the number of multiple strokes per unit time), the circulating flow rate of the processing liquid can be grasped, and from this, the fluctuation of the circulating flow rate can be grasped by the fluctuation of the operating speed. In other words, if there is an abnormal fluctuation in the operating speed, it is possible to early detect flow path blockages such as filter clogging in the circulation device, leakage of processing liquid, etc. It is also possible to minimize damage to the system. In addition, it is possible to predict the life of the bellows or diaphragm by accumulating the total operating time of the pump.Perform planned maintenance management and replace the bellows etc. before it is damaged. Can be prevented. However, if the pump is electrically driven, such as a motor-driven pump, it is easy to extract the electrical signals that represent the operating conditions, that is, the values of the voltage and current that are input to the motor, and the monitoring thereof is also easy. However, the air-driven pump is preferable to the motor-driven pump for use in a system in which an explosion-proof mechanism is required, for example. Further, for example, when it is used in precision engineering, the generation of dust is extremely disliked, but the motor drive tends to cause dust agitation due to rotation and dust agitation due to heat generation and convection. Pneumatic drive is preferred. However, in an air-driven pump, it is difficult to perform a monitoring that sufficiently or directly controls air pressure input to the pump as a driving force with sufficiently high precision, and there has been no effective monitoring system in the past.

[Object of the Invention]

The present invention has been devised in order to effectively solve these problems in view of the problems of the prior art as described above. It is therefore an object of the invention to provide a monitoring device which makes it possible to monitor a circulation system having an air driven pump.

[Means for solving problems]

The monitoring device of the circulation system according to the present invention has the following configuration in order to solve the problems of the conventional technology and achieve the object. That is, in order to alternately perform expansion / contraction motions of two flexible expansion / contraction film members such as bellows or diaphragms, the expansion / contraction film members are respectively connected to both ends thereof and a shaft member for performing a piston motion in the axial direction is provided. In a chemical liquid circulating system including an air-driven pump driven by driving air pressure, the drive air pressure supply system includes a switching valve that alternately switches the driving air pressure and a main valve that supplies and stops the driving air pressure. The air-driven pump is provided in the inner space of the film material and outside of the casing of the air-driven pump in order to release the fluctuating pressure in the expansion film material caused by the expansion and contraction movement of the expansion film material to the atmospheric pressure side. An air escape groove is formed to communicate with and is inserted into the air escape groove from the outside of the casing, and the An electrode sensor that outputs a chemical liquid leak detection signal and closes the main valve is installed so as to face the inner space of the membrane material, and it is detected that the shaft member is at each dead center position of the piston movement, and the detection signal is detected. A position sensor is installed to output, and the operating speed of the air driven pump is calculated based on the detection signal of the position sensor,
A signal generating means for outputting a display signal of the operating speed and an alarm generating means for issuing an alarm based on the leak detection signal of the electrode sensor are provided. Further preferably, the signal generating means is a frequency dividing means for generating one pulse signal for each reciprocating movement of the air driven pump based on the detection signal, and the number of multiple strokes per unit time from the pulse signal. And a calculating means for calculating the number of double strokes calculated above is determined whether or not it is between a preset upper limit value and a lower limit value, and the number of double strokes outside these limit values is a predetermined time or more. A control means for outputting an alarm generation command signal to the alarm generation means in the case of continuous operation and a display means for displaying the number of multiple strokes per unit time are provided. The control means includes a comparison circuit and a timer circuit,
The upper limit value and the lower limit value are set in the comparison circuit, and the predetermined time is set in the timer circuit.

[Action]

According to the monitoring device for the circulation system of the present invention,
The electrode of the electrode sensor can be inserted into the film material by utilizing the air escape groove that absorbs the pressure fluctuation in the expansion / contraction film material. On the other hand, when damage such as cracks occurs in the film material and the chemical liquid leaks into the film material, the chemical liquid tends to flow out from the air escape groove along with the flow of air in the film material. At this time, the electrode sensor installed in this groove is immersed in the chemical liquid and becomes conductive, and outputs a leak detection signal of the chemical liquid. Further, this detection signal acts as a command signal for issuing an alarm to the alarm generation means, and also as an instruction signal for closing the main valve installed in the drive air pressure supply system, Immediately stop the operation by stopping the supply of driving air pressure to the pump. That is, it acts as an emergency stop signal. The core wire of this electrode sensor is
When the chemical solution is strong acid or strong alkaline, gold or platinum is used, and a fluorine resin is used for the coating, which will not be attacked. In addition, the position sensor detects that the shaft member that performs the piston motion to alternately expand and contract the two film materials is at each dead center position, and outputs the detection signal. The detection signal faithfully reflects the expansion / contraction motion of the expansion / contraction film material and is hardly affected by disturbance, so that the signal generating means outputs a monitor signal that more accurately reflects the state of the system. The signal output from this signal generating means is highly reliable and can be used as an input signal for managing the operating state of the system by automatic control. That is, even if the air-driven pump is used, it is possible to perform monitoring with less influence of disturbance, and it is possible to reduce malfunctions in control operation due to the influence of disturbance.

【Example】

A preferred embodiment of the present invention will be described below with reference to FIGS.
It will be described with reference to the drawings. First, with reference to FIG. 1, a schematic configuration of a circulation system in which monitoring is performed by a monitor device according to the present invention will be described. In the figure, reference numeral 1 denotes a processing tank for cleaning semiconductor wafers and the like, which is formed of a material that is not eroded by a cleaning chemical solution and does not elute metals. It may be made of fluororesin, fluororesin lining, quartz, or the like, but those conventionally used for this kind of treatment are used. The chemical solution for treatment is not limited, but in the case of semiconductor wafers, concentrated sulfuric acid and concentrated sulfuric acid containing hydrogen peroxide are generally used at 80 to 150 ° C. Since the chemical solution is gradually contaminated with impurities, the chemical solution is treated by the excess means 2 and cleaned to obtain a treatment solution. An air-driven pump 3 made of perfluorinated resin is used as a conveying means for pressure-feeding the treatment liquid from the treatment tank 1 to the excess means 2. In particular, in this embodiment, a bellows pump is used as a specific example thereof. As another example, a diaphragm pump may be used instead of the bellows pump. The processing liquid (liquid) cleaned by the passing means 2 is returned to the processing tank 1. Further, as shown in FIG. 1, when the treatment liquid contains a volatile substance such as hydrogen peroxide-containing sulfuric acid, a gas separator 4 and a needle valve 5 are provided between the passing means 2 and the treatment tank 1. Is provided, and the processing liquid accumulated in the gas separator 4 is returned to the processing tank 1. Also,
The separated vaporized gas is discharged to the outside through the exhaust pipe 6. The bellows pump 3, as shown in the schematic configuration of FIG. 2, has an actuating portion 7 at substantially the center thereof, and a pair of substantially symmetrical bellows 8 and 8 ′ arranged at both ends of the actuating portion 7 are provided in a casing 9. Pump chambers 10 and 1 that are partitioned and formed at both ends inside
By alternately expanding and contracting (expanding and contracting) within 0 ', discharge pressure and suction pressure are generated. 11, 12, 13, 1 in the figure
4 is a check valve, 15 is an inlet, and 16 is an outlet. When one of the bellows 8 ′ is contracted and the other of the bellows 8 is extended, the check valves 11 and 13 are opened and the other check valves 12 and 14 are closed so that the processing liquid to be pumped is the suction port 1.
5 through the check valve 13 into the one pump chamber 10 ', and the processing liquid in the other pump chamber 10 passes through the check valve 11 and the discharge port 16 through the pass means 2 (shown in FIG. 1). )
Pumped to. The check valve 1 which is closed at this time
Reference numerals 2 and 14 fulfill the rectification function by preventing backflow on the discharge side and the suction side, respectively. When the bellows 8 and 8'reversely operate, the respective check valves 11, 12, 13 and 14
Similarly, the processing liquid is sucked in through the suction port 15 and pressure-fed from the discharge port 16 to the above-mentioned passing means 2. The expansion and contraction movements of the bellows 8 and 8'are driven by axially pistoning the shaft member 17 whose both ends are fixed to the inside of the tip end portions of the bellows 8 and 8 '. The piston motion of the shaft member 17 is caused by the casing-side partition wall portion 18 that holds the substantially central portion of the shaft member 17 in an airtight and slidable manner and the shaft member 17 that is located on both side portions of the casing-side partition wall portion 18. In the two pressure chambers 20 and 20 'that are formed between the shaft-side partition wall portion 19 that extends radially outwardly and the peripheral edge portion of which is in airtight sliding contact with the inner peripheral surface of the casing 9. It is driven by applying driving air pressure. Position sensors 21 and 21 'are installed in the operating portion 7 to extract a signal indicating the motion situation of the bellows pump 3 driven in this way and perform monitoring, and the shaft member 17 is configured to move in each piston movement. When the dead point position is reached, the fact is detected and the detection signal is output. That is, this detection signal is output to the signal generating means 37 (shown in FIG. 6) described later as a signal representing the stroke condition of the bellows pump 3, that is, the driving condition. Further, since the volume of the inner space of the bellows 8, 8'changes with the expansion and contraction motion of the bellows 8, 8 ', the pressure fluctuation of the inner space of the bellows 8, 8'which accompanies this changes is absorbed, so that it is opened to the atmospheric pressure side. The air escape item 22 is formed. In the figure, 23 is a drive air pressure supply system,
24 is the switching valve, and 25 is the main valve. FIG. 3 is an enlarged half-section front view of essential parts showing the detailed structure of the bellows pump 3 shown in FIG. Hereinafter, only one of the left and right symmetrical objects will be described. The shaft member 17 is connected at its left and right symmetrical ends to the center of the inner surface of the head 27 of each bellows 8, 8 '(one is not shown) via a connecting bush 26. By the piston movement within 9, the bellows 8 and 8 ′ alternately expand and contract. A disc-shaped pressure receiving portion 19 is formed on the shaft member 17 as a partition wall on the shaft side for receiving driving air pressure so as to participate in driving the shaft member 17. The bellows 8
The disc diameter is set so that the pressure receiving area is larger than the area of the head portion 27 of the bellows 8 in order to increase the discharge pressure. The casing 9 including the disc-shaped pressure receiving portion 19 and holding the piston movement of the shaft member 17 and the expansion and contraction movement of the bellows 8 while retaining them includes a central drum portion 28, a first cylinder portion 29, and a second cylinder portion 29 described below. The cylinder 54 and the holding portion 30 are composed of four main components. First, in the central portion of the casing 9, the central portion of the shaft member 17 (the connecting portion between the pair of left and right disc-shaped pressure receiving portions) is slidably and airtightly held, and the driving air pressure inlet port 32 is provided. A drum unit 28 is provided. Although not shown in FIG. 3, various mechanisms for switching the supply of the driving air pressure to the left and right of each operating portion structure are housed in the central drum portion 28. A first cylinder portion 29 is provided adjacent to both sides of the central drum portion 28, and an end surface of the central drum portion 28 serves as a casing side partition wall portion 18, which forms a disc shape with the inner peripheral surface of the first cylinder portion 29. A pressure chamber 20 is formed by the pressure receiving portion 19. That is, the disc-shaped pressure receiving portion 19 of the shaft member 17 has its peripheral side surface slidably contacting the inner peripheral surface of the first cylinder portion 29 while being sealed between the inner peripheral surface and the inner peripheral surface of the first cylinder portion 29, and the piston movement is performed to expand or contract the pressure chamber 20. do. As shown in FIG. 3, the first cylinder portion 29 is roughly composed of a tubular portion 34 and a board portion 35, and the end portion of the shaft member 17 slides at the center of the board portion 35. Holds freely. Further, a bellows 8 is housed in the second cylinder portion 54 adjacent to the first cylinder portion 29, and a pump chamber 10 for sucking and discharging the processing liquid is formed. And this second
A ring-shaped holding portion 30 is provided which is fitted to the peripheral portion of the cylinder portion 54 and which is fastened and fixed to the first cylinder portion 29. The bolt 31 is used as the fastening means.
Is used. Each component of these casings 9 is
Airtightness must be maintained at each assembly portion, and strength that can withstand a strong tightening force such as the bolt 31 is required. Therefore, components such as the bellows 8 and the second cylinder portion 54 other than the portion that comes into contact with the processing liquid are formed of stainless steel that is resistant to temperature changes, and in particular, the first cylinder portion 29 should not be damaged. The surface thereof is coated with a fluororesin in order to prepare for leakage of the processing liquid. For fixing the bellows 8 to the casing 9, the flange portion 33 formed by radially extending outward at the end of the bellows 8 is the first.
It is performed by being clamped between the cylinder portion 29 and the second cylinder portion 54 and clamped. further,
On the inner peripheral surface side of the flange portion 33, an annular convex portion 36 projecting from the disc-shaped portion 35 of the first cylinder portion 29 is in contact along the same. This is the first cylinder part 2 by the holding part 30.
9 and the second cylinder portion 54 is tightened by the flange portion 3
Since it acts diagonally outward in the radial direction with respect to 3, the flange portion 33 has a structure for preventing the flange portion 33 from gradually shifting inward in the radial direction while the bellows 8 repeats expansion and contraction movements. That is, not only is the flange portion 33 widened to increase the sealing surface, but also the frictional force is increased to prevent the inward inclination of the flange portion 33. Next, the structure of the disc-shaped portion 35 of the first cylinder portion 29 will be described. FIG. 4 is a side view of the first cylinder portion 29 of this embodiment as viewed from the board-like portion 35 side. As shown in the drawing, a boss portion 47 is formed at the center for supporting the shaft member 17 by inserting it. The holes formed in three places around the boss portion 47 account for most of the air pressure fluctuation in the bellows 8 due to the expansion and contraction of the bellows 8 in the plate-shaped portion 3 in the first cylinder portion 29.
5 is a communication item 49 for allowing the gas to escape to a chamber 48 formed between the disc-shaped pressure receiving portion 19 of the shaft member 17 and the disc-shaped pressure receiving portion 19. These communication items 49 may cause damage to the bellows 8,
Alternatively, even if the airtightness of the flange portion 33 of the bellows 8 is broken and the processing liquid flows into the bellows 8 by any chance, the processing liquid does not flow into the chamber 48 side through the communication item 49. All three are formed at a high position above the center. Reference numeral 36 in the figure denotes an annular convex portion that annularly protrudes along the inner peripheral surface side of the flange portion 33 of the bellows 8, and extends inward from the annular convex portion toward the center from the lowermost end portion of the disc portion 35. Up to this point, the air release groove 22 is formed as the air release item 22 described above, which opens the air pressure fluctuations in the bellows 8 that cannot be released by the communication item 49 to the atmospheric pressure. Further, an electrode sensor 51 having two platinum core wires 50, 50 is inserted in the air escape groove 22. In this electrode sensor 51, as shown in FIG. 5, each core wire 50, 50 is covered with a tube 52 of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) to prevent air in the bellows. The coating tube 52 is exposed to the extent that the tips thereof do not come into contact with each other under the influence of the flow, and the exposed portion faces the air in the bellows and is positioned in the air escape groove 22. Therefore, when a treatment liquid leaks due to cracks or pinholes in the bellows 8, the treatment liquid flowing into the bellows 8 flows downward in the direction of gravity through the air escape groove 22 as the air in the bellows flows. Attempt to flow out of the casing 9. Platinum and fluororesin are strong acids
It is stable against strong alkaline chemicals and will not be attacked. The core wires 50, 50 are electrically conducted when immersed in the processing liquid due to the leakage of the processing liquid, and thus the relay unit
The contact point (not shown) is cut off, and the main valve 25 of the solenoid valve installed in the drive air pressure supply system 23 is closed. Therefore, the operation of the bellows pump 3 is automatically stopped together with the leak of the processing liquid, and it is possible to prevent the leak from further developing. Further, the respective wires covered with the PFA tube 52 are bundled into one and further covered with a heat-shrinkable PFA tube 53. It should be noted that the air escape groove 22 extends radially inward from the outer peripheral end and slightly overlaps the annular projection for the purpose of only absorbing the pressure fluctuation in the bellows 8 (in the figure, It is sufficient to extend up to (shown by a virtual line), but in this case, the core wires 50, 5
Since the tip of 0 is located extremely close to the wall surface of the annular convex portion 36, there is a risk of contact with this wall surface and malfunctioning. To prevent this, the air escape groove 22 penetrates the annular convex portion 36. And extends further inward. Next, a monitoring system in the circulation device including the bellows pump 3 configured as described above will be described. As shown in FIG. 6, the signals from the position sensors 21, 21 ′ of the bellows pump 3 are output to the signal generating means 37. This signal is for detecting the actual piston movement of the shaft member 17, and has much less disturbance than that for detecting the fluctuation of the driving air pressure. Moreover, each dead point in the piston movement of the shaft member 17 is detected. Is output as a pulse signal, that is, a digital signal. Therefore, since two pulse signals are output for one stroke, this is regarded as a signal for one stroke. Therefore, the signals from the position sensors 21, 21 are first of all the lip flop circuit 38 as the frequency dividing means. Entered in. This flip-flop circuit 3
The pulse signal divided by 8 is further driven by the driving means 44 for driving the switching valve and the digital tachometer 3 as the computing means.
The number of outputs per unit time is calculated and calculated as the number of multiple strokes per unit time. The calculated number of multiple strokes is displayed by an appropriate display means 40 which receives the output signal of the digital tachometer 39. Further, since it is possible to judge whether the operating condition of the bellows pump 3 or the system is abnormal or normal from the number of double strokes per unit time, the output signal of the digital tachometer 39 outputs the comparison circuit 42 and the timer circuit 43. It is output to the control means 41 provided. Each of the upper limit value and the lower limit value is set in advance in the comparison circuit 42 as an appropriate range of the number of multiple strokes, and it is always determined whether or not the number of multiple strokes during operation is within the appropriate range. . In addition, the timer circuit 43
In order to determine whether or not the number of multiple strokes becomes abnormal for a certain period of time or more, a predetermined time corresponding to this certain time is set. When the above operation is continued, the control means 41 outputs a signal for instructing the alarm generation means 46 to issue an alarm,
The alarm generation means 46 issues an alarm by this signal. Since the signal input to the flip-flop circuit 38 is a signal indicating that the shaft member 17 is at each dead center position thereof, the drive air pressure supply system is based on the signal switched by the flip-flop circuit 38. It is possible to switch 23 switching valves 24. Therefore, in this embodiment, the output signal from the flip-flop circuit 38 is input to the drive means 44 of the switching valve 24. As described above, in the monitor device of this embodiment, the flip-flop circuit 38 as the frequency dividing means, the digital tachometer 39 as the arithmetic means, the display means 40, and the control means 41 generate signals. Means 37 are configured. In addition to the digital tachometer 39, an integrator 45 can be added as an arithmetic means.
It is also possible to display the total number of multiple strokes (cumulative operating time) of the bellows pump 3 by self-holding the integrated value of the pulse signal at 5, and to predict the service life of the bellows 8 and 8'and determine the maintenance cycle. However, it is also useful for preventive maintenance. Further, when the fluctuation of the pulse signal interval is too large, the control means 41 sets an appropriate time zone, takes a moving average of the signals during that time, and issues an alarm when the value exceeds a predetermined value. It may be set to. Further, the main valve 25 may be closed at the same time when an alarm is issued by a signal output from the control means 41. Further, in the above-described embodiment, the electrode sensor 51 is provided only in the air escape groove 22 of the bellows pump 3. However, when the bellows pump 3 and the passing means 2 are constructed as one unit, the housing 55 of the unit is formed. (6th
It may also be provided at other places where there is a risk of leakage of the processing liquid, such as being provided at the bottom part (schematically shown in the figure).

【The invention's effect】

As is clear from the above description, according to the present invention, the following excellent effects are exhibited. That is, in a circulation overpass system having an air-driven pump, highly accurate monitoring with less influence of disturbance can be performed, and in particular, when an abnormality occurs in the operating state of the pump, this can be immediately known by an alarm and the circulation overpass can be detected. It is possible to take measures to prevent system failures and the like. In addition, even if the flexible expansion / contraction membrane material of the bellows or diaphragm, which is the most leak-prone part of the air-driven pump, is damaged, such as cracks or pinholes, it is immediately detected and an alarm is issued and the pump Since the operation is forcibly stopped, it is possible to prevent the damage from spreading. In this way, it is possible to comprehensively manage both the normal state and the abnormal state of the circulation system having the air-driven pump.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a circulation system which is monitored by a monitor device according to the present invention, and FIG. 2 is a schematic diagram showing a schematic configuration of a bellows pump used in this embodiment, and FIG. FIG. 4 is an enlarged half-section front view of an essential part showing the detailed structure of the bellows pump shown in FIG. 2, FIG. 4 is a side view of the first cylinder portion of FIG. Is a perspective view showing a schematic configuration of a tip portion of an electrode sensor of a bellows pump used in this embodiment, and FIG. 6 is a block diagram showing a schematic configuration of a monitor device of this embodiment. 3 ... Bellows pump as an air driven pump, 8, 8 '
... Bellows as expansion / contraction film material, 9 ... Pump casing, 17 ... Shaft member 21, 21 '... Position sensor,
22 ... Air escape groove, 23 ... Driving air pressure supply system, 24
... switching valve, 25 ... main valve, 37 ... signal generating means, 38
... Flip-flop circuit as frequency dividing means, 39 ... Digital tachometer as arithmetic means, 40 ... Display means, 41
... control means, 42 ... comparison circuit, 43 ... timer circuit, 46
... Alarm generating means, 51 ... Electrode sensor

Claims (3)

[Claims] 1. An axial direction in which two flexible expansion / contraction membrane materials (8, 8 ′) such as a bellows or a diaphragm are alternately connected to both ends in order to alternately perform expansion / contraction motions. A circulating fluid system for chemical liquids, comprising a shaft member (17) for piston movement, and an air driven pump (3) in which the piston movement of the shaft member (17) is driven by driving air pressure. (23) is provided with a switching valve (24) for alternately switching the drive air pressure and a main valve (25) for supplying / stopping the drive air pressure, and the air drive pump (3) is provided with the expansion / contraction membrane material. (8,8 ') in order to allow the fluctuating pressure in the expansion / contraction membrane material (8,8') that accompanies the expansion / contraction motion to escape to the atmospheric pressure side, the inner space of the membrane material and the casing of the air driven pump (3) ( Air escape groove that communicates with the outside of 9)
(22) is formed, is inserted into the air escape groove (22) from the outside of the casing (9), outputs a leak detection signal of the chemical liquid in a conductive state, and closes the main valve (25). The electrode sensor (51) is installed so as to face the inner space of the film material, and the shaft member (17) detects that each dead center position of the piston movement, and outputs a detection signal (21, 21 ') is installed, the signal generating means for calculating the operating speed of the air driven pump (3) based on the detection signal of the position sensor (21, 21'), and outputting a display signal of the operating speed (37 ) And the electrode sensor (5
A monitoring device for a circulation excess system, comprising: an alarm generating means (46) for issuing an alarm based on the leak detection signal of 1). 2. The signal generating means (37), a frequency dividing means (38) for generating one pulse signal for each reciprocating movement of the air driven pump (3) based on the detection signal, Arithmetic means (39) for calculating the number of multiple strokes per unit time from the pulse signal, the calculated number of multiple strokes, it is determined whether or not between a preset upper and lower limit value, Control means (41) for outputting an alarm generation command signal to the alarm generation means (46) when the number of multiple strokes outside these limit values continues for a predetermined time or longer
And a display means (40) for displaying the number of multiple strokes per unit time
The monitoring device for the circulation system according to claim 1, further comprising: 3. The control means (41) includes a comparison circuit (42) and a timer circuit (43), the upper limit value and the lower limit value are set in the comparison circuit, and the predetermined time is the timer circuit (43). The monitoring device for a circulation system according to claim 2, wherein the monitoring device is set to.