JP2634665B2 - Temperature control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides a refrigerator and a heater for a temperature control target tank in a thermostat, a thermo-hygrostat, and other environmental test devices. The present invention relates to a temperature control method for controlling the temperature in the bath by controlling the heater output while operating the heater.

[Conventional technology]

In a temperature control method of providing a refrigerator and a heater for a temperature control target tank in an environmental test device or the like and controlling the heater output while controlling the heater output while operating the refrigerator, The refrigerant flow rate or the degree of opening of the expansion mechanism is set to a constant state in advance so that the refrigerator can be operated even in a somewhat high-temperature atmosphere.

However, once the refrigeration circuit is determined under these setting conditions,
When trying to raise the temperature in the tank at a predetermined gradient toward the target temperature, the amount of circulating refrigerant may not be easily increased to the target temperature due to too much, or the heater output must be increased, resulting in a large energy loss. Problem. In addition, if the amount of circulating refrigerant is reduced to solve this problem, a problem arises in that the allowable heat load in the tank is reduced.

Further, when trying to lower the temperature at a predetermined gradient, there is a case where the amount of circulating refrigerant is too small and does not readily drop to the target temperature. In addition, if the amount of circulating refrigerant is increased to solve this problem, the refrigerator, particularly the compressor discharge side, becomes dangerous.

Therefore, in the case of the slope operation, the ascending slope, the descending slope,
It is desirable to set the minimum opening of the expansion mechanism of the refrigerator to an appropriate opening according to the temperature of the gradient or the like. Also, by doing so, the range of the gradient can be expanded.

[Problems to be solved by the invention]

However, there is another problem even if the minimum opening is appropriately set at the start of the gradient operation. That is, when shifting from the operation at the preceding stage to the next gradient operation, the temperature rise line or the fall line fluctuates and becomes unstable, and it is often difficult to start a desired gradient operation.

In addition, there is a problem that the range of selectable gradients is limited when trying to avoid such an unstable state.

Therefore, the present invention provides a temperature control method in which a refrigerator is provided for a temperature control target tank and a heater is provided, and the temperature of the tank is controlled by controlling the heater output while operating the refrigerator. It is an object of the present invention to provide a method capable of performing a desired gradient operation control that can be selected from a range and has as little disturbance or fluctuation as possible in a temperature rising line or a falling line.

[Means for solving the problem]

According to the present invention, there is provided a temperature control method for providing a refrigerator to a temperature control target tank, providing a heater, and controlling the heater output while operating the refrigerator to control the temperature in the tank. The variable opening degree expansion mechanism is adopted as the expansion mechanism of the refrigerator, and when the next operation is the gradient operation, the smaller allowable opening degree of the expansion mechanism is determined in advance suitable for switching to the next gradient operation. The temperature control method is characterized by determining the allowable opening Mmin.

The predetermined opening degree Mmin is fixed based on an experiment or predetermined as a function of the gradient so that a smooth transition to the next gradient operation or a smooth start of the next gradient operation can be achieved. It is. The smaller allowable opening Mmin
Does not need to be the minimum allowable opening, but an opening that is normally considered to be the minimum or an opening close to it is selected.

(Operation)

According to the method of the present invention, when the next operation is an operation of raising or lowering the temperature in the temperature control target tank at a constant gradient, the smaller allowable opening of the expansion valve for smoothly shifting to the next gradient operation. The degree is determined, and the currently set operation is performed so that the opening degree of the expansion valve does not become smaller than the opening degree.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic explanatory view of an example of an apparatus for carrying out the method of the present invention, and FIGS. 5 to 9 show procedures including an example of the method of the present invention performed by the apparatus.

The example of the device shown in FIG.
1 has a test area 102 for accommodating a specimen, and an air conditioning room 104 is provided behind the area via a partition wall 103. The air-conditioning room is provided with a cooler 11 and a fan for air circulation above it.
It has twelve. An electric heater 2 as a heating heater is provided between the cooler 11 and the fan 12, and an evaporative humidifier 30 of a type for heating water by an electric heater 3 for humidification is provided below the cooler. I have. The air circulates in the direction of arrow A by the action of the fan 12. The cooler 11 is a constituent member of the refrigerator 1. The refrigerator 1 is provided with a compressor 13, a condenser 14, and a variable opening type electronic expansion valve 15 for the cooler 11, in addition to the cooler 11, in addition to the cooler 11.

The valve 15 is of a type in which when a shaft (not shown) is turned, the valve body moves and the valve opening changes. The shaft is driven by a stepping motor 41, and a pulse output generator 42 is connected to the motor 41. This generator 42 is a microcomputer M
(Hereinafter referred to as “microcomputer M”).

A current supply circuit 21 is connected to the heater 2, and a current supply circuit 31 is connected to the humidification heater 3. These circuits 21 and 31 operate based on an instruction from the microcomputer M.

The motor M1 that drives the fan 12 passes through the drive circuit C1,
The drive motor M3 of the compressor motor M2 and the fan 141 for the condenser 14 are connected to the microcomputer M via a drive circuit C2.

In the tank 101, a dry bulb temperature detector 5 and a wet bulb temperature detector 6 are provided near the outlet of the air conditioning room 104, and the outputs of these detectors are input to the microcomputer M. Further, a temperature detector 7 for measuring the ambient temperature is arranged in the air flow flowing into the condenser 14 in the refrigerator 1, and a temperature signal from the detector is also input to the microcomputer M. Further, a temperature detector 9 for detecting a refrigerator abnormality is provided in a discharge pipe of the compressor 1, and a signal from the detector is also input to the microcomputer M.

An operation board 8 including a numeric keypad and the like is connected to the microcomputer M, and a mode of a temperature operation, a temperature / humidity operation, or a gradient operation can be selected by the board 8. In the case of the temperature and humidity operation, the target temperature and humidity can be set, and in the case of the gradient operation, the temperature at the start of the gradient operation, the temperature at the end of the gradient operation, and the time required therebetween can be set to set the temperature change gradient. Further, the order of various operations can be input as appropriate. That is, for example, at 50 ° C. and 60% RH for 3 hours,
The operating sequence can be set to drop to 20 ° C. in 2 hours, then 3 hours at 20 ° C., 60% RH.

The board 8 further includes a fan motor M1, a compressor motor M2, and a fan motor M3 for starting the operation of the thermo-hygrostat 10.
There is also provided an instruction key for starting operation of the like or stopping them.

Next, the method of the embodiment of the present invention executed in such a thermo-hygrostat will be described.

According to the thermo-hygrostat shown in FIG. 1, in the case of temperature operation,
That is, in the case of an operation for maintaining the temperature of the tank 101, or more precisely, the test area 102 at the target temperature, the dry-bulb temperature detector 5 moves the inside of the test area 102 toward the target temperature (set temperature) indicated on the board 8. The output of the heater 2 is controlled based on an instruction from the microcomputer M while monitoring the temperature.

Also, in the case of the gradient operation, the output of the heater 2 is controlled according to the temperature change gradient instructed on the board 8.

In the case of the temperature / humidity operation, that is, the operation of maintaining the temperature and humidity (target temperature / humidity) set on the board 8 in the tank 101, more precisely, in the test area 102, the temperature / humidity in the test area 102 is detected. The outputs of the heating heater 2 and the humidifying heater 3 are controlled based on instructions from the microcomputer M while being monitored by the heaters 5 and 6. In any case, the operation key 8 on the operation board 8 is used to instruct the fan 12 and the refrigerator 1 to start operating.

In addition, the valve 15 is opened and closed as necessary, based on an instruction from the microcomputer M, as will be described later, in any case.

The main routine of the control by the microcomputer M is as shown in FIG.

First, when the program is started, initialization for initialization of the microcomputer M is performed in step Sa. Next, in step Sb, a man-machine interface process, that is, a process of writing the information instructed and input on the board 8 to the memory is performed. Thereafter, a control process is performed in step Sc, and the process returns to step Sa again.

When a timer interrupt is generated from a timer IC (not shown) at predetermined time intervals (step Sd), first, a timer management process is performed in step Se, then the output of the heater is controlled in step Sf, and the expansion valve is controlled in step Sg. The opening is controlled and the refrigerator (particularly the motor M
2, M3) Control the operation and return.

The timer management processing routine in step Se is as shown in FIG. 3. First, in step Se1, the counter is updated, and in step Se2, it is determined whether or not a predetermined time s has been reached. If the time has been reached, the timer flag is set to "1" in step Se3, and the timer counter is reset in step Se4.

The control processing of the subroutine Sc shown in the main routine is as shown in FIG.

First, in step Sc1, it is determined whether or not the timer flag is "1". If it is "1", the counter C is determined in step Sc2.
Are updated, and if C = 1 in step Sc3, step S
Proceed to c4 to perform temperature control calculation processing. C in step Sc3
If ≠ 1, it is determined whether or not C = 2 in step Sc5. If C = 2, the process proceeds to step Sc6, where a humidity control calculation process is performed, and then the counter is reset in step Sc7. Regardless of whether the process proceeds to step Sc4 or (Sc6, Sc7), the process proceeds to step Sc8, where the expansion valve opening process is performed, the timer flag is set to “0” in step Sc9, and the process returns to the main routine. If the timer flag is not "1" in step Sc1, the process immediately returns to the main routine.

The essential part of the method of the embodiment of the present invention is executed in the expansion valve opening control in step Sc8 in the interrupt routine Sd based on this processing and the expansion valve opening processing in step Sc8 in this control processing routine.

Therefore, the method of the embodiment of the present invention will be described based on a flowchart showing an outline of an expansion valve opening degree processing routine shown in FIG. 5 to FIG.

First, in step S1, reading whether the refrigerator 1 is on or off is performed, and in step S2, an alarm check is performed. This alarm check is for detecting an abnormality of the refrigerator 1. In this embodiment, a temperature signal from the temperature detector 9 for measuring the discharge pipe temperature of the compressor 13 is read.

Next, in step S3, the presence or absence of an alarm is determined. In this example, in this example, it is determined whether or not the discharge pipe temperature t is higher than a predetermined safe temperature t1. If “YES”, the discharge pipe temperature is abnormal, so the process proceeds to step S4.

In step S4, the temperature t is a predetermined dangerous temperature.
It is determined whether or not t2 has been reached. If t2 has been reached, the compressor is immediately stopped in step S5, and the refrigerator 1 is stopped in step Sh in the timer interrupt routine Sd.
However, if the discharge pipe temperature t is smaller than t2, step S6
Then, it is determined that the expansion valve 15 is closed by a predetermined amount. Based on this determination, the expansion valve is closed in step Sg of the timer interrupt routine Sd. This operation of closing the expansion valve is repeated until the discharge pipe temperature t becomes equal to or lower than the predetermined safety limit temperature t1.

Now, if it is determined in step S3 that the discharge pipe temperature t is a safe temperature, it is determined in step S7 whether the refrigerator is on,
If it is off, it is determined in step S8 whether the zero reset has been completed. If the zero reset has been completed, the routine immediately returns. If not, the zero reset is performed in step S9. This zero reset issues a command to completely close the expansion valve 15 when the refrigerator is not operating. Based on this zero reset, the expansion valve is closed in step Sg in the interrupt routine Sd.

If the refrigerator is on in step S7, the process proceeds to step S10, where it is determined whether or not the next operation set on the board 8 is a gradient operation. If the next operation is not the gradient operation, it is determined in step S11 whether the state in the test area 102 of the thermo-hygrostat is stable. That is, whether the target temperature set on the board 8 is stable within a range of the error ± a ° C. if the operation is the temperature operation, and if the target temperature is within the range of the error ± a ° C. in the case of the temperature and humidity operation. And whether the set target humidity is stable within the range of error ± b% RH. Alternatively, it is determined whether or not the vehicle is currently running on a slope. If the result of these determinations in step S11 is "NO", the steps shown in FIG.
Proceed to S12.

In steps S12 to S151, the maximum allowable opening Mmax of the expansion valve 15 in the refrigerator 1 under the current ambient temperature RT and the current tank temperature T is determined.

There are various methods for obtaining Mmax. Here, Mmax is obtained from the ambient temperature RT and the tank temperature T. The ambient temperature RT is obtained by the temperature detector 7 shown in FIG. 1, and the tank temperature T is obtained by the temperature detector 5 shown in FIG. Step S13
Then, from the maximum allowable opening of the expansion valve, which was previously obtained by variously changing the chamber temperature T and the ambient temperature RT by experiments,
When the ambient temperature RT is determined, an equation X that can calculate the maximum allowable opening Mmax of the expansion valve 15 with respect to the tank temperature T is obtained. In this example, the relational expression X is obtained as a linear expression.

That is, Mmax = a × T + b (primary expression X), and a =
f (RT), b = f (RT).

After the relational expression X is obtained in this way, it is determined in step S14 whether the temperature should be increased or the temperature should be decreased toward the set temperature (target temperature).

Temperature Lowering Process In the case of the temperature lowering process, the process proceeds to step S151, in which the maximum allowable opening Mmax of the expansion valve under the temperature T is calculated by substituting the current tank temperature T into the expression X.

Then determine the difference between P ₂ between the current opening degree N of the maximum permissible opening Mmax and the expansion valve of the expansion valve at step S16. Then I asked first
Depending on the sign of P _2, it determines the opening and closing of the expansion valve (step S17).

Next, in step S18, the minimum valve opening Mmin allowable in the temperature lowering process is selected and determined according to the type of operation, that is, the temperature operation or the temperature and humidity operation. Such a minimum allowable opening is selected from among the minimum allowable openings predetermined in accordance with the type of operation and stored in the memory.

In addition, Mmin in the temperature lowering process is such that oil flowing together with the refrigerant in the refrigeration circuit is not clogged at the valve portion,
The determination is made in consideration of, for example, that the low pressure side pressure of the circuit does not become abnormally low and that the amount of circulating refrigerant is small, but that a certain amount flows without fluctuation.

After determining the minimum allowable opening Mmin in this way,
In S19, it is determined whether or not the current valve opening N is between Mmax and Mmin. If so, in step S20, the valve operation amount Pm = |
Outputs the open command of P ₂ |.

If the determination in step S19 is "NO", step S21
It is determined whether or not the current valve opening N is greater than Mmax. If it is larger, a command to close the valve is output up to Mmax. Otherwise, that is, if N <Mmin, Mmin is determined in step S23.
Outputs the command to open the valve until.

The reason for judging Mmin <N <Mmax, Mmax <N, and N <Mmin is that Mmax <Mmax
This is because <N or N <Mmin may be satisfied.

The instructions issued in each of steps S20, S22 and S23 are executed in the expansion valve control process of step Sg in the timer interrupt routine Sd shown in FIG.

Thus, in the temperature drop control in the thermo-hygrostat 10,
It is safe to consider the maximum allowable opening Mmax of the expansion valve 15 allowed under the current ambient temperature RT and the current tank temperature T, and also consider the predetermined minimum allowable opening Mmin of the expansion valve. Thus, the opening of the expansion valve 15 can be controlled so as to approach the set temperature (target temperature).

Temperature raising process Now, if it is determined in step S14 that the process is a temperature raising process, the process proceeds to step S152, where the target temperature T ₀ in the bath is substituted into the equation X obtained in the previous step S13, and the temperature is raised. T
The maximum allowable opening Mtmax at ₀ is obtained.

Then determine the maximum allowable opening Mmax of the expansion valve at the present time is allowed on the basis of a difference ΔT of the current tank temperature T and intracisternal set temperature (target temperature) T ₀ in step S24, then step
S25 in determining the difference P ₃ between the Mmax and the current expansion valve opening N.
The method of obtaining Mmax here will be described later. In step S26, P ₃
The valve open or the valve close is determined according to the positive or negative sign of.

Thereafter, the process proceeds to step S18 in the same manner as in the case of the temperature drop control described above, in which the minimum allowable opening suitable for the temperature increase control operation is selected from the minimum allowable opening Mmin of the valve predetermined according to the type of operation. Determine the degree Mmin.

After that operation quantity Pm = at step S20 in accordance with the magnitude relationship between the current opening degree N and Mmin and Mmax | P ₃ | or outputs an instruction of valve opening or valve closing in accordance with the valve in step S22 until Mmax Output a close command or output a command to open the valve to Mmini in step S23.

This instruction is executed in the expansion valve control of step Sg in the timer interrupt routine Sd.

The minimum allowable opening Mm of the valve in the temperature rise control
in is also determined from the same viewpoint as the valve minimum allowable opening in the temperature drop control.

The current maximum allowable valve opening degree Mmax allowed under the difference ΔT between the current in-chamber temperature T and the in-chamber target temperature T ₀ makes the allowable heat load in the chamber as large as possible even in the temperature rise control, and as a definition so that it can reach as soon as possible the target temperature, can be considered a variety of defined way, the maximum allowable opening Mtmax a function of the temperature difference ΔT in this case under the current ambient temperature RT and the target temperature T ₀ Asking. That is, Here, ΔT = T−T ₀ k is a correction coefficient determined in advance depending on whether control is performed in consideration only of temperature or control in consideration of humidity, and a temperature settable range; for example, −10 to 50 ° C.

As described above, in the temperature rise control operation, the maximum allowable opening Mmax of the expansion valve that can be currently opened is determined in consideration of the difference ΔT between the current temperature in the tank and the target temperature in the tank. Suddenly the maximum allowable opening Mtma at the target chamber temperature T ₀
If x is set, the adverse effect that the temperature rise rate in the bath becomes slow is prevented. When the target temperature is reached, a large allowable heat generation load is obtained. In addition, in opening and closing the expansion valve, the current opening N and the maximum allowable opening Mma are set after step S19.
Since the magnitude relationship between x and the minimum allowable opening Mmin is taken into consideration, the expansion valve opening can be controlled more appropriately and safely.

In the case where the next operation is the gradient operation Now, the process returns to step S10. Step S10 (fifth
If the next setting is determined to be slope operation in Figure),
Proceeding to step S27, it is determined here whether or not the operation is an ascending gradient operation. In the case of the ascending gradient operation, a predetermined fixed expansion valve allowable minimum opening Mmin is determined in step S271.

This opening Mmin is determined by a suitable heater at any temperature rise so that a smooth transition from the current operation to the next gradient operation is possible, i.e., a stable uphill operation without disturbance can be entered immediately. This is the opening that has been confirmed by experiment to obtain an output.

If the next setting is the descending gradient operation, the process proceeds to step S28, where the gradient is calculated from the temperature TS at the start of operation, the temperature TE at the end of operation, and the operation control time MN by the following equation.

Next, in step S29, an expansion valve minimum allowable opening Mmin = f (gradient) suitable for the gradient is calculated. This equation is desirably determined so that the gradient can be selected from the widest possible range, and various possibilities are conceivable.Here, based on experiments, it is assumed that there is no abnormality in the refrigerant circuit and a smooth transition to the next set descent gradient operation can be performed. Set forth in

That is, in this example, Mmin = Mp × gradient + Mq. Here, Mp and Mq are constants, and have a relationship of Mp> Mq.

After determining the minimum allowable opening Mmin of the expansion valve when the next operation is the gradient operation in step S27 or S29, the process proceeds to step S30.

Here select determines the operation amount P ₁ corresponding to the type of the current operating out of a single operation of the expansion valve is predetermined according to the type of operation.

Next, in step S31, an average heater output value is obtained. Here, the heater refers to the heater 2 during the current temperature operation, and the heater 2 during the current temperature / humidity operation.
And the humidifying heater 3.

The calculation of the heater output average value is performed by a plurality of values measured and stored in the temperature processing subroutine (step Sc4) and the humidity processing subroutine (step Sc6) in the control processing routine Sc shown in FIG. 4 before reaching step S31. It is calculated based on the output value.

After calculating the heater output average value in this way,
Upper limit H of heater output according to current operation type in S32
U and lower limit HD, or the heater output upper and lower limit HU, HD
And an upper limit hu and a lower limit hd of the humidification heater output.

These upper and lower limits are predetermined according to the type of operation so that heater output can be saved as much as possible while smooth control is performed, and are stored in the memory of the microcomputer M.

In the next steps S33 to S36, between the upper and lower limits of the heater output appropriate for the type of the current operation,
That is, it is determined whether or not the heater output is controlled in an appropriate heater output control range, and in the case of “No”, the opening degree of the expansion valve is controlled so that the output is controlled in such an appropriate range. decide.

More specifically, in the case of the current temperature operation or the gradient operation not considering the humidity, step S33 is performed.
In determining whether the heater output average value HA is greater than the heater upper HU, when large decides to close the expansion valve operation amount with P ₁ (step S331). If the value is smaller, the average heater output HA is the upper limit of the heater output.
It is determined whether it is between HU and the lower limit HD, and if it is, it is determined that the valve opening is not adjusted in step S35, and `` NO '', that is, the average value HA is smaller than the lower limit HD It determines the expansion valve opening operation by the operation amount P ₁ in step S36 when.

If the current operation is a temperature-humidity operation or a gradient operation that also considers humidity, in step S33, the heater output average value HA is larger than the heater output upper limit HU, and the humidification heater output average value ha is the humidification heater output upper limit. It is determined whether it is larger than hu, and if “YES”, the process proceeds to step S331, and “N
If "O", the process proceeds to step S34. In step S34, the heater output average value HA is between the upper limit HU and the lower limit HD of the heater output, and the humidification heater output average value ha is between the upper limit hu and the lower limit hd of the humidification heater output. Judge. If "YES", proceed to step S35,
If “NO”, the process proceeds to step S36.

In this way after determining the opening and closing of the expansion valve according to the operation amount P ₁ and steps S37 S39, the sixth current ambient temperature RT definitive when the same approaches to the step S12 from the S151 shown in FIG. And the current tank temperature T The original maximum allowable opening Mmax of the expansion valve is obtained, and thereafter, the process proceeds to step S19 and the subsequent steps described above.

When it is determined in step S10 shown in FIG. 5 that the next setting is the gradient operation, the process proceeds to step S27, and then proceeds to step S19 via step S39, Mmin after step S19 is determined in step S271. Mmi
n or Mmin calculated in step S29,
The operation amount Pm in S20 is the operation amount determined in step S30.
It is a P _1.

If it is determined in step S11 (FIG. 5) that the temperature operation or the temperature / humidity operation is stable or that the vehicle is currently running on a gradient, the process proceeds to step S111 (FIG. 8) where the type of operation is performed. Minimum allowable opening Mm of expansion valve according to
in is determined, and thereafter, the process proceeds to step S30 described above. As described above, even in a stable state in temperature operation or temperature / humidity operation, or in a gradient operation, the heater output is optimized according to the type of operation, and the heater output is saved while performing smooth temperature or temperature / humidity control. Plan.

When the process proceeds from step S11 to step S19 via steps S111 to S39, the minimum allowable opening Mmin of the expansion valve after step S19 is Mmin determined in the previous step S111.

In the procedure described above, in practice, the expansion valve openings Mmax, Mtmax, and Mmin are, respectively, based on the opening of a certain state of the expansion valve, for example, based on a completely closed state.
It is treated as the number of pulses required to reach Mmax, Mtmax, and Mmin. The expansion valve operation amount Pm (P ₁ , P ₂ ,
P ₃ ) is also handled by the number of pulses.

〔The invention's effect〕

According to the present invention, a refrigerator is provided to a temperature control target tank and a heater is provided, and when controlling the heater output while operating the refrigerator to control the temperature in the tank, the gradient is adjusted from a wide range. When selected, the desired gradient operation control can be performed in a stable state with as little disturbance or fluctuation in the temperature rise line or the fall line as possible.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a thermo-hygrostat for carrying out an example of the method of the present invention. FIG. 2 is a flowchart showing a main routine of the operation of the microcomputer M shown in FIG. 1, FIG. 3 is a flowchart showing a timer management routine, and FIG. 4 is a flowchart showing a control processing routine. 5 to 9 are flow charts for explaining the method of the embodiment of the present invention, and are also flow charts showing an expansion valve processing routine shown in FIG. 1 ... refrigerator, 2 ... heater, 3 ... humidification heater, 15 ... electronic expansion valve, 5 ... dry bulb temperature detector, 6 ... wet bulb temperature detector, 7 ... ambient temperature detector , 9: Compressor discharge pipe temperature detector, M: microcomputer, 8: operation board, 10: constant temperature / humidity chamber, 101: tank, 102: test area in the tank.

Claims (1)

(57) [Claims] 1. A temperature control method comprising: providing a refrigerator and a heater for a temperature control target tank; and controlling the heater output while operating the refrigerator to control the temperature in the tank. The variable opening type expansion mechanism is adopted as the expansion mechanism of
If the next operation is a gradient operation, a smaller allowable opening of the expansion mechanism is determined to a predetermined allowable opening Mmin suitable for switching to the next gradient operation.