Patent Description:
In industrial processes, it may be necessary to heat a process medium such as oil, gas or another process fluid, or a solid process medium. In particular, heating of the process medium may be to achieve a target temperature, and/or to maintain the process medium at the target temperature. In such industrial processes a system including an electric heating arrangement may be used for heating the process medium. In particular, the process medium to be heated may be a process fluid.

In use, faults may develop within the system which are associated with a risk of damage to the system itself and/or unintended conduction of electric current to components outside of the system. For instance, faults may arise within the electric heating arrangement of such a system due to failure of a sealing structure around the heating arrangement and, in particular, due to process fluid ingress into the heating arrangement. Damage to the system may occur as a result of thermal damage within the heating arrangement, such as melting of a heating element within the heating arrangement. Unintended conduction of electrical current to components outside of the system may occur as a result of conduction of electric current from the heating arrangement to the components outside of the system through the process medium. Unintended conduction of electrical current to components outside of the system may occur as a result of conduction of electric current from the conductors to the heater through the conductor insulation.

It is desirable to provide a system and a method for heating a process medium which enables the provision of improved safeguards against the risks associated with the development of faults within a heating arrangement of the system.

<CIT> describes an explosion proof forced air electric heater which is designed to supply heat to hazardous areas where the atmosphere contains readily combustible gases, vapors or dust particles. The heater employs an air mover which forces air through a metal heat sink with strategically placed electric heating elements. Terminal ends of the heating elements extend into a sealed and encapsulated explosion proof containment chamber which is connected to a centralized explosion proof enclosure. The explosion proof enclosure contains the control features and the electrical connections of the heater along with external accessories. The heating cycle is controlled via an electronic control circuit. The electronic circuit controls the process heating temperature, air mover operation, heating element operation, temperature measuring device operation, and monitors the total operation time of the heating elements while providing process failure feed back to an operator.

According to a first aspect there is provided a method of controlling a system including a heating arrangement for heating a process medium, a current sensing arrangement, and a switching arrangement configured to selectively couple a power supply to the heating arrangement, the switching arrangement comprising at least one semiconductor switch, the method comprising:
in response to a demand signal for starting heating of the process medium, operating the system in a test mode, wherein operating the system in the test mode includes performing a test sequence comprising:.

Operation of the system in the heating mode may include, in response to a terminate signal for ending heating of the process medium, switching the system from operation in the heating mode to operation in the dormant mode.

It may be that, when coupled to the heating arrangement, the power supply provides a periodic AC electrical power to the heating arrangement. The duration of the predetermined period may be no greater than <NUM>% of a duration of a characteristic time period of the periodic AC electrical power. The duration of the characteristic time period of the periodic AC electrical power may be no greater than <NUM> milliseconds.

Additionally or alternatively, it may be that the predetermined period is defined according to a phase angle range of the periodic AC electrical power, the phase angle range being defined between a first phase angle of the periodic AC electrical power and a second phase angle of the periodic AC electrical power. It may also be that the second phase angle of the periodic AC electrical power is between: <NUM> degrees less than a zero-crossing phase angle of the alternating current electrical power; and the zero-crossing phase angle of the alternating current electrical power. The first phase angle of the AC electrical power may be between <NUM> and <NUM> degrees less than the second phase angle of the AC electrical power.

The duration of the final predetermined period may be greater than the duration of the preliminary predetermined period. It may be that each of the final predetermined period and the preliminary predetermined period is defined according to a phase angle range of the periodic AC electrical power, each phase angle range being defined between a first phase angle of the periodic AC electrical power and a second phase angle of the periodic AC electrical power, and it may be that the first phase angle which defines the preliminary predetermined period is closer to the zero-crossing phase angle of the periodic AC electrical power than the first phase angle which defines the final predetermined period.

It may be that, when coupled to the heating arrangement, the power supply provides a DC electrical power to the heating arrangement, and wherein the system comprises a DC-DC converter, and it may also be that performing the test sequence includes controlling the DC-DC converter to ensure that a magnitude of a DC current of the DC electrical power provided to the heating arrangement is less than a rated current of the switching arrangement throughout the predetermined period.

In addition, it may be that performing the preliminary test sequence includes controlling the DC-DC converter to ensure that a magnitude of a DC current of the DC electrical power provided to the heating arrangement is less than a rated current of the switching arrangement throughout the preliminary predetermined period. It may also be that the magnitude of the DC current through the heating arrangement throughout the preliminary predetermined period is less than the magnitude of the DC current through the heating arrangement throughout the final predetermined period. The DC-DC converter may include a chopper.

Operation of the system in the first dormant mode may include generating an alarm indicative of a fault associated with the heating arrangement.

Additionally, it may be that, when coupled to the heating arrangement, the power supply provides a polyphase periodic AC electrical power to the heating arrangement, and wherein the heating arrangement comprises a plurality of heating elements, each heating element being configured to receive a respective phase of the polyphase periodic AC electrical power from the power supply via the switching arrangement.

According to a second aspect there is provided a data processing apparatus comprising a controller adapted to perform the method of the first aspect.

According to a third aspect there is provided a system comprising: a heating arrangement for heating a process medium; a switching arrangement configured to selectively couple a power supply to the heating arrangement, the switching arrangement comprising at least one semiconductor switch; a current sensing arrangement; and a controller configured to control the system in accordance with the method of the first aspect.

The at least one semiconductor switch may be a transistor or a thyristor. The at least one semiconductor switch may be selected from a group consisting of: a field-effect transistor, a gate turn-off thyristor, integrated-gate bipolar transistor, an integrated gate-commutated thyristor, and an injection-enhanced gate transistor.

According to a fourth aspect there is provided a machine-readable storage medium having stored thereon instructions which, when executed by a controller, cause the controller to carry out the method of the first aspect.

<FIG> shows a first example system <NUM> comprising a switching arrangement <NUM>, a heating arrangement <NUM> for heating a process medium <NUM>, a current sensing arrangement <NUM> and a controller <NUM>. <FIG> shows a second example system <NUM>' which is generally similar to the first example system <NUM>, with like reference signs indicating common or similar features. <FIG> shows a third example system <NUM>" which is generally similar to the first example system <NUM>, with like reference signs indicating common or similar features. The differences between each of the first example system <NUM>, the second example system <NUM>' and the third example system <NUM>" are explained in detail below.

The switching arrangement <NUM> is generally configured to selectively couple a power supply <NUM> to the heating arrangement <NUM>. When the power supply <NUM> is coupled to the heating arrangement <NUM> by the switching arrangement <NUM>, the power supply <NUM> provides electrical power to the heating arrangement <NUM> for heating the process medium <NUM>. The heating arrangement <NUM> is configured to convert electrical power supplied from the power supply <NUM> via the switching arrangement <NUM> into heat by means of an Ohmic heating process within a heating element of the heating arrangement <NUM>. Heat is then transferred to the process medium <NUM> as a result of conduction, convection and/or radiation, as will be appreciated by those skilled in the art. When the power supply <NUM> is decoupled from (e.g. isolated from) the heating arrangement <NUM> by the switching arrangement <NUM>, the power supply <NUM> does not provide electrical power to the heating arrangement <NUM>.

To selectively couple the power supply <NUM> to the heating arrangement <NUM>, the switching arrangement <NUM> comprises at least one semiconductor switch. Conventional switches (e.g. mechanical or other non-semiconductor switches) may generally have a higher rated current than the semiconductor switches of the example systems of the present disclosure. In use, the heating arrangement <NUM> may generally require the supply of a relatively large electric current to adequately heat the process medium <NUM>. Consequently, existing systems typically make use of non-semiconductor switches for the purpose of selectively coupling and/or decoupling a power supply to a heating arrangement. However, use of at least one semiconductor switch 120A within the switching arrangement <NUM> enables selective coupling and/or decoupling of the power supply <NUM> and the heating arrangement <NUM> to be executed more rapidly compared to non-semiconductor switches.

To this end, the at least one semiconductor switch 120A-120C may be, for example, a transistor or a thyristor. In particular, the or each semiconductor switch may be a field-effect transistor, a gate turn-off thyristor, integrated-gate bipolar transistor, an integrated gate-commutated thyristor, and/or an injection-enhanced gate transistor. Use of such types of semiconductor switches as a part of the switching arrangement <NUM> may provide more robust means for selectively coupling and/or decoupling the power supply <NUM> from the heating arrangement <NUM>, which is associated with an extended lifetime of the system <NUM>, <NUM>', <NUM>".

In both the first example electrical system <NUM> and the second example electrical system <NUM>', the power supply <NUM> is an alternating current (AC) power supply <NUM>. Accordingly, when the power supply <NUM> is coupled to the heating arrangement <NUM> by the switching arrangement <NUM>, the power supply <NUM> provides a periodic AC electrical power to the heating arrangement <NUM>.

In the example of <FIG>, the power supply <NUM> is a monophase AC power supply <NUM>. Therefore, when the power supply <NUM> is coupled to the heating arrangement <NUM> by the switching arrangement <NUM>, the power supply <NUM> provides a monophase periodic AC electrical power to the heating arrangement <NUM>. The switching arrangement <NUM> comprises a single semiconductor switch 120A, while the heating arrangement <NUM> comprises a single heating element 130A.

In the example of <FIG>, with respect to the second example system <NUM>', the power supply <NUM> is a polyphase AC power supply <NUM>. Therefore, when the power supply <NUM> is coupled to the heating arrangement <NUM> by the switching arrangement <NUM>, the power supply <NUM> provides a polyphase periodic AC electrical power to the heating arrangement <NUM>. The switching arrangement <NUM> comprises a plurality of semiconductor switches 120A-120C. The heating arrangement <NUM> comprises a plurality of heating elements 130A-130C. Although the power supply <NUM> is shown as being a three-phase AC power supply in the example of <FIG>, those skilled in the art will appreciate that the principles described herein apply to similar systems provided with polyphase AC power supplies having any suitable number of phases. In the specific example of <FIG>, the plurality of semiconductor switches includes a first semiconductor switch 120A, a second semiconductor swich 120B, and a third semiconductor switch 120C. Further, the plurality of heating elements 130A-130C includes a first heating element 130A, a second heating element 130B, and a third heating element 130C. Each heating element 130A-130C is configured to receive a respective phase of the polyphase electrical power provided by the power supply <NUM> via a corresponding semiconductor switch 120A-120C of the switching arrangement <NUM>. Each phase of the polyphase electrical power is different to each other phase of the polyphase electrical power. The supply of a respective phase of a polyphase electrical power to the heating arrangement <NUM> enables a smoother transfer of heat from the heating arrangement <NUM> to the process medium <NUM>, because there is never any point in time, in use, when the applied voltage or the applied current within the heating arrangement <NUM> is zero.

In the example of <FIG>, the power supply <NUM> is a direct current (DC) power supply <NUM>. It follows that, when the power supply <NUM> is coupled to the heating arrangement <NUM> by the switching arrangement <NUM>, the power supply <NUM> provides a DC electrical power to the heating arrangement <NUM>. Additionally, the third example system <NUM>" comprises a DC-DC converter <NUM> configured to convert a DC electric current received from the power supply <NUM> having a first current magnitude into a DC electric current for supply to the heating arrangement <NUM> via the switching arrangement <NUM> having a second current magnitude. The first current magnitude may generally be dissimilar to (i.e. different from) the second current magnitude. Accordingly, the DC-DC converter <NUM> is operable to control the magnitude of the DC electric current supplied to the heating arrangement <NUM> when the heating arrangement <NUM> is coupled to the power supply <NUM> by the switching arrangement <NUM>. For this purpose, the DC-DC converter <NUM> may preferably comprise a chopper 150A. This may ensure particularly efficient and effective conversion of the DC currents received from the power supply <NUM> and provided to the heating arrangement <NUM>, respectively, by the DC-DC converter <NUM>. The chopper 150A may be a step-up chopper or a step-down chopper.

In each of the example systems <NUM>, <NUM>', <NUM>", the current sensing arrangement <NUM> is adapted to monitor an electric current through the heating arrangement <NUM>. In the second example system <NUM>', the current sensing arrangement <NUM> may be adapted to monitor an electric current through each of the heating elements 130A-130C of the heating arrangement <NUM>. Specific types of circuitry suitable for use within the current sensing arrangement <NUM> for the purpose of monitoring the electric current through the heating arrangement <NUM> will be known to those skilled in the art. Also, in each of the example systems <NUM>, <NUM>', <NUM>", the controller <NUM> is in data communication with the current sensing arrangement <NUM> by means of a wired and/or a wireless data connection. The controller <NUM> is also configured to control the switching arrangement <NUM> in each of the example systems <NUM>, <NUM>', <NUM>". In the third example system <NUM>", the controller <NUM> is further configured to control the DC-DC converter <NUM>. The controller <NUM> is configured to control the system <NUM>, <NUM>', <NUM>" in accordance with the example method described below with reference to <FIG>.

<FIG> is a flowchart which shows an example method <NUM> of controlling a system in accordance with any of the example systems <NUM>, <NUM>', <NUM>" described above with reference to <FIG>. Specific implementations of the method <NUM> in the context of the individual example systems of <FIG> are highlighted in the description below.

In general terms, the method <NUM> comprises selectively operating the system <NUM>, <NUM>', <NUM>" in at least a dormant mode, a test mode (at block <NUM>) and a heating mode (at block <NUM>). In the example of <FIG>, the method <NUM> comprises a plurality of dormant modes, the plurality of dormant modes including a first dormant mode (at block <NUM>) and a second dormant mode (at block <NUM>). The first dormant mode <NUM> may be referred to as a locked dormant mode <NUM>, whereas the second dormant mode <NUM> may be referred to as a standby dormant mode. However, this disclosure is not limited to the use of two dormant modes, but also anticipates there being only a single dormant mode. If the method <NUM> includes a only single dormant mode, the dormant mode is the standby dormant mode <NUM> as shown in <FIG> and described herein.

The or each dormant mode <NUM>, <NUM> includes controlling the switching arrangement to decouple the power supply <NUM> from the heating arrangement <NUM>. As a consequence, in the or each dormant mode <NUM>, <NUM>, the power supply <NUM> does not provide electrical power to the heating arrangement <NUM> and therefore the heating arrangement <NUM> does not heat the process medium <NUM>.

The method <NUM> includes selectively switching between operating the system <NUM>, <NUM>' <NUM>" in each of the modes as illustrated by arrows <NUM>, <NUM>, <NUM>, <NUM> and <NUM> extending between respective blocks <NUM>-<NUM>. The criteria for switching between each of the modes are explained below with reference to <FIG>, which show the exemplary contents of blocks <NUM>-<NUM> in detail. Typically, the method <NUM> is initiated by operating the system <NUM>, <NUM>', <NUM>" in the standby dormant mode <NUM>.

<FIG> is a flowchart which shows steps of an example method for operation of a system <NUM>, <NUM>', <NUM>" in the standby dormant mode <NUM> (that is, the second dormant mode <NUM>) in detail. Operation of the system in the standby dormant mode <NUM> includes, at block <NUM>, controlling the switching arrangement <NUM> to decouple the power supply <NUM> from the heating arrangement <NUM>. As a consequence, in operation of the system in the standby dormant mode <NUM>, the power supply <NUM> does not provide electrical power to the heating arrangement <NUM> and therefore the heating arrangement <NUM> does not heat the process medium <NUM>.

Operating the system <NUM>, <NUM>', <NUM>" in the standby dormant mode <NUM> further comprises determining, at block <NUM>, whether a demand signal for heating the process medium <NUM> has been received. The demand signal is related to a requirement to heat the process medium <NUM>. The demand signal may be received from, for example, a centralised control system which is in data communication with the controller <NUM>. Otherwise, the demand signal may be received from a user-interface provided to the system according to, for example, a manual input from an operator.

In response to a determination that the demand signal has not been received at block <NUM>, operating the system <NUM>, <NUM>', <NUM>" in the standby dormant mode <NUM> includes returning to block <NUM>, such that the switching arrangement <NUM> continues to be controlled to decouple the power supply <NUM> from the heating arrangement <NUM>.

Conversely, in response to a determination that the demand signal has been received at block <NUM>, operating the system <NUM>, <NUM>', <NUM>" in the standby dormant mode <NUM> includes switching the system <NUM>, <NUM>', <NUM>" from the standby dormant mode <NUM> to the test mode <NUM>, as shown by arrow <NUM> on <FIG>, <FIG>, <FIG> and <FIG>. In this way, the standby dormant mode <NUM> is responsive to a receipt of the demand signal for heating the process medium <NUM>. In broad terms, the method <NUM> comprises operating the system <NUM>, <NUM>', <NUM>" in the test mode <NUM> in response to the demand signal at block <NUM>.

<FIG> is a flowchart which shows steps of an example method for operating the system <NUM>, <NUM>', <NUM>" in the test mode <NUM> in detail. In the example of <FIG>, operating the system <NUM>, <NUM>', <NUM>" in the test mode <NUM> includes performing a performing a plurality of test sequences. The plurality of test sequences include a preliminary test sequence (at block 230A) and a final test sequence (at block 230B). Nevertheless, in other examples in accordance with the present disclosure, operating the system in the test mode <NUM> may include performing only a single test sequence 230A (that is, the preliminary test sequence 230A as described herein). In such examples, the preliminary test sequence 230A may be simply referred to as the test sequence 230A. In examples comprising both the preliminary test sequence 230A and the final test sequence 230B, performance of the preliminary test sequence 230A precedes (e.g. is chronologically before) any performance of the final test sequence 230B.

<FIG> is a flowchart which shows steps of an example method for performing the preliminary test sequence 230A shown in <FIG> in detail. The preliminary test sequence includes at least process 232A, process 234A, and process 236A. In the example of <FIG>, the method includes <NUM> performing the final test sequence 230B following (i.e. chronologically after) performance of the preliminary test sequence 230A, as shown by arrow <NUM> on <FIG> and <FIG>. However, if the test mode <NUM> only comprises the preliminary test sequence 230A, the method <NUM> includes performing the preliminary test sequence 230A immediately after operating the system <NUM>, <NUM>', <NUM>" in a dormant mode (e.g. the standby dormant mode).

Process 232A includes controlling the switching arrangement <NUM> to couple the power supply <NUM> to the heating arrangement <NUM> for a duration of a preliminary predetermined period. The power supply <NUM> provides electrical power to the heating arrangement <NUM> for the duration of the preliminary predetermined period as a consequence of process 232A. At the end of the preliminary predetermined period, process 232A includes controlling the switching arrangement to decouple the power supply <NUM> from the heating arrangement <NUM>.

Process 234A comprises monitoring an electric current through the heating arrangement <NUM> during (and continuously throughout) the preliminary predetermined period. If the heating arrangement <NUM> comprises a plurality of heating elements <NUM>, as in the second example system <NUM>', process 234A may include monitoring an electric current through each of the plurality of heating elements 130A-130C. The electric current through the heating arrangement <NUM> is monitored using the sensing arrangement <NUM> as described above. Process 236A includes comparing, during the preliminary predetermined period, the monitored electric current through the heating arrangement <NUM> to a preliminary electric current threshold. If the test mode <NUM> only includes the preliminary test sequence 230A, the preliminary predetermined period may be simply referred to as the predetermined period and the preliminary electric current threshold may simply be referred to as the electric current threshold.

If the monitored electric current (through the heating arrangement <NUM> or each of the heating elements 130A-130C) meets or exceeds (i.e. is equal to or greater than) the preliminary electric current threshold at any point in time during the preliminary predetermined period, performing the preliminary test sequence 230A includes switching the system <NUM>, <NUM>', <NUM>" from the test mode <NUM> to a dormant mode, as shown by arrow <NUM> on <FIG>, <FIG>, <FIG>. If the system <NUM>, <NUM>', <NUM>" is capable of operating in the locked dormant mode and the standby dormant mode, the method <NUM> includes switching the system <NUM>, <NUM>', <NUM>" from operation in the test mode <NUM> to operation in the locked dormant mode <NUM>. On the other hand, if the system <NUM>, <NUM>', <NUM>" is only capable of operating in the standby dormant mode, the method <NUM> includes switching the system <NUM>, <NUM>', <NUM>" from operating in the test mode <NUM> to operation in the standby dormant mode <NUM>. In either case, the method <NUM> does not proceed to operating the system <NUM>, <NUM>', <NUM>" in the heating mode <NUM> if the monitored electric current meets or exceeds the preliminary electric current threshold at any point in time during the preliminary predetermined period.

Otherwise, if the monitored electric current does not meet the preliminary electric current threshold at any point in time during the preliminary predetermined period (i.e. if the monitored current remains below the preliminary electric current threshold for the duration of the preliminary predetermined period), performing the preliminary test sequence 230A further comprises a step of switching the system <NUM>, <NUM>', <NUM>" to performing the final test sequence 230A, as shown by arrow <NUM> in <FIG> and <FIG>, or a step of switching the system <NUM>, <NUM>', <NUM>" into the heating mode <NUM>, as shown by arrow <NUM> in <FIG>, <FIG> and <FIG> (depending on whether the method <NUM> includes performing both the final test sequence 230B and the preliminary test sequence 230A or only the preliminary test sequence 230A).

If the power supply <NUM> is a DC power supply <NUM> and the system <NUM>" comprises a DC-DC converter <NUM>, as shown in the third example system <NUM>", the preliminary test sequence 230A is specifically implemented so as to also include a process 231A. In turn, process 231A comprises controlling the DC-DC converter <NUM> so as to ensure that a magnitude of the DC current of the DC electrical power provided to the heating arrangement <NUM> is less than a rated current of the switching arrangement <NUM> throughout the preliminary predetermined period. This ensures that the switching arrangement <NUM> is able to decouple the power supply <NUM> from the heating arrangement <NUM> at the end of the preliminary predetermined period without suffering damage or a failure. This may be of particular importance because the switching arrangement <NUM> comprises at least one semiconductor switch 120A. As mentioned above, the rated current of semiconductor switches may generally be lower than the rated current of conventional types of switches (e.g. non-semiconductor switches). Therefore, controlling the DC-DC converter <NUM> in this manner may reduce a mean time between failures and thereby extend a service lifetime of the system <NUM>".

If the power supply <NUM> is an AC power supply <NUM>, as shown in the first example system <NUM> and the second example system <NUM>', the preliminary test sequence 230A may be implemented in a variety of ways. Specific example implementations of the preliminary test sequence 230A for use in the context of a system <NUM>, <NUM>' comprising an AC power supply are explained below with reference to <FIG>, which is an annotated graph <NUM> which shows a simplified profile <NUM> of the voltage of one phase of the periodic AC electrical power provided by the AC power supply <NUM> on the y-axis against the phase (in degrees, °) of the periodic AC electrical power on the x-axis. The simplified profile <NUM> shown in <FIG> is intended to aid understanding of the test mode <NUM> described herein, and is not intended to closely correspond to a true profile of one phase AC electrical power provided by the AC power supply <NUM> in typical operation.

In broad terms, the duration of the preliminary predetermined period is intentionally very short. This ensures that, even if a fault is present within the heating arrangement <NUM>, the supply of electrical power to the heating arrangement <NUM> for the preliminary predetermined period is unlikely to result in (further) damage to the system <NUM>, <NUM>' and/or significant unintended conduction of electric current to components outside of the system. However, the supply of electrical power to the heating arrangement <NUM> for the preliminary predetermined period may enable a fault which is present within the heating arrangement <NUM> to be detected before the system <NUM>, <NUM>', <NUM>" is operated in the heating mode <NUM> (or switched into the final test sequence 230B, if applicable). In addition, the supply of electrical power to the heating arrangement <NUM> for the preliminary predetermined period may promote at least partial drying of the heating element(s) 130A-130B of the heating arrangement <NUM> if fluid (e.g. process fluid <NUM>) has come into proximity of or into contact with the heating arrangement <NUM> due to ingression of fluid into the heating arrangement <NUM>. For comparison, methods not in accordance with the present disclosure may proceed directly from, for example, the standby dormant mode <NUM> to the heating mode <NUM>. However, if fluid has come into proximity of or into contact with the heating arrangement <NUM>, moving directly to coupling of the power supply <NUM> to the heating arrangement <NUM> at block <NUM> in response to receipt of the demand signal at block <NUM> may result in damage to the system <NUM>, <NUM>' and/or significant unintended conduction of electric current to components outside of the system before the heating element(s) 130A-130B of the heating arrangement <NUM> were adequately dried.

More specifically, the duration of the preliminary predetermined period may be defined according to the properties of the periodic AC electrical power provided by the AC power supply <NUM> in use. The periodic AC electrical power provided by the AC power supply <NUM>, in operation, has a characteristic time period (e.g. the AC time period) which is the mathematical reciprocal of a characteristic frequency (e.g. the AC frequency). The duration of the preliminary predetermined period may be no greater than <NUM>% of a duration of the characteristic time period of the periodic AC electrical power. In general, the AC electrical power may have a characteristic frequency of no less than <NUM>, and so the characteristic time period of the periodic AC electrical power may be no greater than <NUM> milliseconds. Accordingly, the duration of the preliminary predetermined period may be no greater than <NUM> milliseconds. Preferably, the duration of the preliminary predetermined period may be no greater than <NUM>% of a duration of the characteristic time period of the periodic AC electrical power, such that the duration of the preliminary predetermined period is no greater than <NUM> milliseconds. Application of these criteria ensures that the duration of the preliminary predetermined period is defined so as to ensure that the supply of electrical power to the heating arrangement <NUM> for the preliminary predetermined period is unlikely to result in (further) damage to the system <NUM>, <NUM>' and/or significant unintended conduction of electric current to components outside of the system.

Additionally or alternatively, the preliminary predetermined period may be defined according to a phase angle range <NUM> of the periodic AC electrical power provided by the AC power supply <NUM>, as shown on <FIG>. The phase angle range <NUM> is defined between a first phase angle φ<NUM> of the periodic AC electrical power <NUM> and a second phase angle φ<NUM> of the periodic AC electrical power <NUM>. This means that the AC power supply <NUM> is coupled to the heating arrangement <NUM> at the first phase angle φ<NUM> and decoupled from the heating arrangement <NUM> at the second phase angle φ<NUM>.

Both the first phase angle φ<NUM> and the second phase angle φ<NUM> are relatively close to a zero-crossing phase angle <NUM> (i.e. the zero-crossing point) of the periodic AC electrical power <NUM>, with the second phase angle φ<NUM> being relatively closer to the zero-crossing phase angle <NUM> than the first phase angle φ<NUM>. In some examples, the second phase angle φ<NUM> may be at the zero-crossing phase angle <NUM>. This timing of the selective coupling and decoupling of the AC supply <NUM> to and from the heating arrangement <NUM> ensures that the voltage applied to the heating arrangement during the preliminary predetermined period is significantly less than the peak voltage (that is, the maximum amplitude) of the periodic AC electrical power <NUM>. This is generally associated with improved safety during the test mode <NUM>, and may also ensure that the current through the heating arrangement <NUM> is less than the rated current of the switching arrangement <NUM> throughout the preliminary predetermined period.

The second phase angle φ<NUM> of the periodic AC electrical power <NUM> may be between: <NUM> degrees less than the zero-crossing phase angle <NUM> and the zero-crossing phase angle <NUM> of the periodic AC electrical power <NUM>. Preferably, the second phase angle φ<NUM> of the periodic AC electrical power <NUM> may be between: <NUM> degrees less than the zero-crossing phase angle <NUM> and the zero-crossing phase angle <NUM> of the periodic AC electrical power <NUM>. More preferably, the second phase angle φ<NUM> of the periodic AC electrical power <NUM> may be between: <NUM> degrees less than the zero-crossing phase angle <NUM> and the zero-crossing phase angle <NUM> of the periodic AC electrical power <NUM>. It may even be that the phase angle φ<NUM> of the periodic AC electrical power <NUM> is approximately equal to the zero-crossing phase angle <NUM> of the periodic AC electrical power <NUM>.

The first phase angle φ<NUM> of the periodic AC electrical power <NUM> may be between <NUM> and <NUM> degrees less than the second phase angle φ<NUM> of the periodic AC electrical power <NUM>, such that the phase angle range <NUM> is between <NUM> and <NUM> degrees. Preferably, the first phase angle φ<NUM> of the periodic AC electrical power <NUM> may be between <NUM> and <NUM> degrees less than the second phase angle φ<NUM> of the periodic AC electrical power <NUM>, such that the phase angle range <NUM> is between <NUM> and <NUM> degrees. More preferably, the first phase angle φ<NUM> of the periodic AC electrical power <NUM> may be between <NUM> and <NUM> degrees less than the second phase angle φ<NUM> of the periodic AC electrical power <NUM>, such that the phase angle range <NUM> is between <NUM> and <NUM> degrees.

Specification of the predetermined period in accordance with the phase angle range criteria <NUM> described above ensures that the voltage of the periodic AC electrical power is decaying throughout the phase angle range <NUM> and therefore the preliminary predetermined period. Advantageously, even if the coupling and/or decoupling function provided by the switching arrangement <NUM> is delayed (i.e. is associated with a lag-time) in use, the voltage of the periodic AC electrical power is likely to remain significantly lower than the peak voltage (that is, the maximum amplitude) of the periodic AC electrical power <NUM> throughout the preliminary predetermined period. As discussed above, this is associated with improved safety of the system <NUM>, <NUM>' and may also help ensure that the current through the heating arrangement <NUM> is less than the rated current of the switching arrangement <NUM> throughout the preliminary predetermined period.

<FIG> is a flowchart which shows an example final test sequence 230B shown in <FIG> in detail. The final test sequence 230B is generally similar to the preliminary test sequence 230A, with like reference numerals differentiated by the suffixes A and B indicating similar features.

Process 232B includes controlling the switching arrangement <NUM> to couple the power supply <NUM> to the heating arrangement <NUM> for a duration of a final predetermined period. Like the duration of the preliminary predetermined period, the duration of the final predetermined period is intentionally very short. However, the duration of the final predetermined period and the duration of the preliminary predetermined period may be dissimilar, as explained in further detail below.

Process 234B comprises monitoring an electric current through the heating arrangement <NUM> during (and continuously throughout) the final predetermined period using the sensing arrangement <NUM>. Process 236B includes comparing, during the final predetermined period, the monitored electric current through the heating arrangement <NUM> to a final electric current threshold. The magnitude of the final electric current threshold and the magnitude of the preliminary electric current threshold are different for the reasoning set out further below.

If the monitored electric current meets or exceeds the final electric current threshold at any point in time during the final predetermined period, performing the final test sequence 230B includes switching the system <NUM>, <NUM>', <NUM>" from the test mode <NUM> to a dormant mode, as shown by arrow <NUM> on <FIG>, <FIG>, <FIG>. In a similar way to the procedure described above in respect of the final test sequence 230A, depending on whether the system <NUM>, <NUM>', <NUM>" is capable of operating in the locked dormant mode and the standby dormant mode, the method <NUM> either includes switching the system <NUM>, <NUM>', <NUM>" from operation in the test mode <NUM> to operation in the locked dormant mode <NUM> or to operation in the standby dormant mode <NUM>.

On the other hand, if the monitored electric current does not meet the final electric current threshold at any point in time during the final predetermined period (i.e. if the monitored electric current remains below the final electric current threshold for the duration of the final predetermined period), performing the final test sequence 230B includes a step of switching the system <NUM>, <NUM>', <NUM>" into the heating mode <NUM>, as shown by arrow <NUM> in <FIG>, <FIG> and <FIG>.

The or each electric current threshold is selected to correspond to an expected upper limit for the magnitude of the electric current through the heating arrangement <NUM> during the respective predetermined period if the heating arrangement <NUM> is not in a fault condition. If the monitored electric current meets or exceeds the relevant electric current threshold at any point during the respective predetermined period, this may generally be indicative of the presence of a fault within the heating arrangement <NUM> or indicative of the heating element(s) 130A-130B of the heating arrangement <NUM> having being wetted by, for example, the process fluid <NUM>. For instance, it may be that a short-circuit fault within the heating arrangement <NUM> has developed since the system <NUM>, <NUM>', <NUM>" was last operated, which causes the monitored electric current to be higher than expected during performance of the preliminary test sequence 230A or the final test sequence 230B. The method <NUM> therefore takes action to prevent the system <NUM>, <NUM>', <NUM>" from being operated in the heating mode <NUM> in response to the monitored electrical current meeting or exceeding the relevant electric current threshold at any point during the respective predetermined period. The method <NUM> switches the system <NUM>, <NUM>', <NUM>" into a dormant mode, which may be the locked dormant mode <NUM> or the standby dormant mode <NUM>, as discussed above.

If operating the system <NUM>, <NUM>', <NUM>" in the test mode <NUM> includes performing the final test sequence 230B, the final and preliminary electric current thresholds are dissimilar. Because the final predetermined period is longer than the preliminary predetermined period and/or the magnitude of the DC current through the heating arrangement throughout the final predetermined period is greater than the magnitude of the DC current through the heating arrangement throughout the preliminary predetermined period, the final electric current threshold is greater than the preliminary electric current threshold.

In particular, if the power supply <NUM> is an AC power supply <NUM> and the preliminary predetermined period is defined by a phase angle range <NUM> as discussed above with reference to <FIG>, the final predetermined period may be similarly defined by a phase angle range <NUM>. However, the final predetermined period may be defined by a larger phase angle range than the preliminary predetermined period. For instance, if the final predetermined period is defined by a phase angle range <NUM> of approximately <NUM> degrees, the preliminary predetermined period may be defined by a phase angle range <NUM> of approximately <NUM> degrees. The first phase angle φ<NUM> and the second phase angle φ<NUM> may be determined accordingly to appropriately define each of the preliminary predetermined period and the final predetermined period.

Further, if the power supply <NUM> is an AC power supply <NUM>, the duration of the final predetermined period is longer than the duration of the preliminary predetermined period. As a particular example, if the final predetermined period is defined by a phase angle range <NUM> as discussed in the above paragraph, the first phase angle φ<NUM> of the phase angle range <NUM> which defines the preliminary predetermined period may be closer to the zero-crossing phase angle <NUM> than the first phase angle φ<NUM> of the phase angle range <NUM> which defines the final predetermined period. In addition, the second phase angle φ<NUM> of the phase angle range <NUM> which defines the preliminary predetermined period may be chosen so that the phase angle range <NUM> which defines the preliminary predetermined period is equal to or smaller than the phase angle range <NUM> which defines the final predetermined period. This results in the phase angle range <NUM> which defines the final predetermined period being larger than the phase angle range <NUM> which defines the preliminary predetermined period.

This specification of the timing of the selective coupling and decoupling of the AC supply <NUM> to and from the heating arrangement <NUM> in the respective test sequences 230A, 230B ensures that the voltage applied to the heating arrangement <NUM> during the preliminary predetermined period is always less than the voltage applied to the heating arrangement <NUM> during the final predetermined period. In turn, this may facilitate safer performance of the test sequence <NUM> and/or better drying of the heating arrangement <NUM> during the test sequence <NUM>.

If the power supply <NUM> is a DC power supply <NUM> and the system <NUM>" comprises a DC-DC converter <NUM>, as shown in the third example system <NUM>", the final test sequence 230B is specifically implemented so as to also include a process 231B. Process 231B is generally comparable to process 231A in that it similarly comprises controlling the DC-DC converter <NUM> so as to ensure that a magnitude of the DC current of the DC electrical power provided to the heating arrangement <NUM> is less than a rated current of the switching arrangement <NUM> throughout the final predetermined period, for similar reasoning as given above in reference to process 231A.

However, the magnitude of the electric current through the heating arrangement <NUM> during (and continuously throughout) the preliminary predetermined period is less than the magnitude of the electric current through the heating arrangement <NUM> during (and continuously throughout) the final predetermined period. The DC-DC converter <NUM> may be specifically controlled by the controller <NUM> to this end. This may facilitate effective drying of the heating element(s) 130A-130C during the final test sequence 230B prior to operation of the system <NUM>, <NUM>', <NUM>" in the heating mode <NUM>.

Performance of both the final test sequence 230B and the preliminary test sequence 230A in the test mode <NUM> may allow for incremental drying of the heating arrangement <NUM> during the method. Performance of the final test sequence 230B may allow the heating element(s) of the heating arrangement <NUM> to be (further) dried by evaporation prior to operation of the system <NUM>, <NUM>', <NUM>" in the heating mode <NUM> in addition to any partial drying in the preliminary test sequence 230A. If the heating element(s) of the heating arrangement <NUM> had not been dried as a result of performance of the final test sequence 230B, the wet condition of the heating arrangement <NUM> may have resulted in adverse electrical effects (e.g. significant unintended conduction of electric current to components outside of the system <NUM>, <NUM>', <NUM>") if the system <NUM>, <NUM>', <NUM>" were operated in the heating mode <NUM>. Therefore, the performance of both test sequences enables more reliable and effective operation of the system <NUM>, <NUM>', <NUM>". Moreover, the heating arrangement <NUM> being in a fault condition may be detected in the preliminary test sequence 230A (which is at a lower voltage) and the system <NUM>, <NUM>' may be moved into a dormant mode without a need to execute the final test sequence 230B (which is at a higher voltage). This is associated with safer operation of the system <NUM>, <NUM>', <NUM>".

<FIG> is a flowchart which shows steps in an example method for operating the system <NUM>, <NUM>', <NUM>" in the locked dormant mode <NUM> (that is, the first dormant mode <NUM>) in detail. Like operating the system <NUM>, <NUM>', <NUM>" in the standby dormant mode <NUM>, operating the system <NUM>, <NUM>', <NUM>" in the locked dormant mode includes, at block <NUM>, controlling the switching arrangement <NUM> to decouple the power supply <NUM> from the heating arrangement <NUM>. As a consequence, when the system <NUM>, <NUM>', <NUM>" is operated in the locked dormant mode <NUM>, the power supply <NUM> does not provide electrical power to the heating arrangement <NUM> and therefore the heating arrangement <NUM> does not heat the process medium <NUM>. In contrast to when the system <NUM>, <NUM>', <NUM>" is operating in the standby dormant mode <NUM>, when operated in the locked dormant mode <NUM>, the system <NUM>, <NUM>', <NUM>" is not responsive to a receipt of the demand signal for heating the process medium <NUM>. In other words, operating the system <NUM>, <NUM>', <NUM>" in the locked dormant mode includes continuing to operate the system <NUM>, <NUM>', <NUM>" in the first non-operation mode <NUM> in response to the demand signal.

In further contrast to operating the system <NUM>, <NUM>', <NUM>" the second dormant mode <NUM>, the operating the system <NUM>, <NUM>', <NUM>" in the locked dormant mode <NUM> comprises determining, at block <NUM>, whether a reset signal has been received. The reset signal may be received from a user-interface provided to the system according to a manual input from an operator. For instance, after performing maintenance on the heating arrangement <NUM> so as to rectify any identified faults, the operator may manipulate the user-interface and thereby cause the reset signal to be provided to the controller <NUM>. In response to a determination that the reset signal has not been received at block <NUM>, operating the system in the locked dormant mode <NUM> includes returning to block <NUM>, such that the switching arrangement <NUM> continues to be controlled to decouple the power supply <NUM> from the heating arrangement <NUM>. Conversely, in response to a determination that the reset signal has been received at block <NUM>, operating the system <NUM>, <NUM>', <NUM>" in the locked dormant mode <NUM> includes switching the system <NUM>, <NUM>', <NUM>" from operating in the locked dormant mode <NUM> to operation in the second dormant mode <NUM>, as shown by arrow <NUM> on <FIG>, <FIG> and <FIG>.

Operating the system <NUM>, <NUM>', <NUM>" in the locked dormant mode <NUM> may also include, at block <NUM>, generating an alarm signal indicative of a fault within the heating arrangement <NUM>. The alarm signal may generally be intended to alert an operator or a maintenance system to the presence of a fault within the heating arrangement <NUM>. The alarm signal may be provided to, for example, a user-interface of the system, a remote monitoring device, and/or a centralised control system by the controller <NUM>. In particular, the alarm signal may result in the activation of an audible, visual and/or tactile alert at the user-interface, the remote monitoring device, and/or the centralised control system. Generating the alarm signal may prompt an operator or maintenance system to perform any required maintenance on the heating arrangement <NUM>, such as replacing or repairing a seal around the heating arrangement <NUM> and/or the individual heating elements 130A-130C, replacing or repairing the individual heating element(s) 130A-130C of the heating arrangement <NUM>, and/or replacing the entire heating arrangement <NUM>. Because operating the system <NUM>, <NUM>', <NUM>" in the locked dormant mode <NUM> includes decoupling the heating arrangement <NUM> from the power supply <NUM>, maintenance may be safely executed while the system <NUM>, <NUM>' <NUM>" is operated in the locked dormant mode <NUM>. Subsequently, the operator may cause the reset signal to be provided to the controller <NUM> as described above, which results in the system <NUM>, <NUM>' <NUM>" being switched into the second dormant mode <NUM> (that is, the standby dormant mode). Accordingly, the system <NUM>, <NUM>', <NUM>' may then be switched into operating in the test mode <NUM> in response to the receipt of the demand signal for heating the process medium <NUM> and, if appropriate, subsequently safely switched into operating in the heating mode <NUM>.

<FIG> is a flowchart which shows steps of an example method for operating the system <NUM>, <NUM>', <NUM>" in the heating mode <NUM> in detail. Operating the system <NUM>, <NUM>', <NUM>" heating mode includes, at block <NUM>, controlling the switching arrangement <NUM> to couple the power supply <NUM> to the heating arrangement <NUM>. Therefore, when the system <NUM>, <NUM>', <NUM>" is operated in the heating mode <NUM>, the power supply <NUM> provides electrical power to the heating arrangement <NUM> and therefore the heating arrangement <NUM> heats the process medium <NUM>. Heating of the process medium <NUM> is to achieve a target temperature and/or to maintain the process medium <NUM> at the target temperature.

Operating the system <NUM>, <NUM>', <NUM>" in the heating mode <NUM> comprises determining, at block <NUM>, whether a terminate signal for ending heating of the process medium <NUM> has been received. The terminate signal may be received from, for example, the centralised control system which is in data communication with the controller <NUM>. Otherwise, the terminate signal may be received from a user-interface provided to the system according to, for example, a manual input from an operator. In response to a determination that the terminate signal has not been received at block <NUM>, operating the system <NUM>, <NUM>', <NUM>" in the heating mode <NUM> includes returning to block <NUM>, such that the switching arrangement <NUM> continues to be controlled so as to couple the power supply <NUM> to the heating arrangement <NUM>. Conversely, in response to a determination that the terminate signal has been received at block <NUM>, operating the system <NUM>, <NUM>', <NUM>" in the heating mode <NUM> includes switching the system <NUM>, <NUM>', <NUM>" from the heating mode <NUM> to the standby dormant mode <NUM>, as shown by arrow <NUM> on <FIG>, <FIG> and <FIG>.

<FIG> highly schematically shows a data processing apparatus <NUM> comprising a controller <NUM> adapted to perform the method described above with reference to <FIG> (and <FIG>). The controller <NUM> may have any of the features of the controller <NUM> described above with respect to <FIG>. <FIG> symbolically shows a machine-readable medium <NUM> having stored thereon a software program <NUM> comprising instructions which, when executed by a controller <NUM> (e.g. the controller <NUM> provided to the example systems <NUM>, <NUM>', <NUM>" described above with reference to <FIG>), cause the controller <NUM> to execute the method <NUM> described above with reference to <FIG> (and <FIG>).

The controller <NUM> described herein may comprise a processor. The controller or processor may comprise: at least one application specific integrated circuit (ASIC); and/or at least one field programmable gate array (FPGA); and/or single or multiprocessor architectures; and/or sequential (Von Neumann)/parallel architectures; and/or at least one programmable logic controllers (PLCs); and/or at least one microprocessor; and/or at least one microcontroller; and/or a central processing unit (CPU), to the stated functions for which the controller or processor is configured.

Claim 1:
A method (<NUM>) of controlling a system (<NUM>, <NUM>', <NUM>") including a heating arrangement (<NUM>) for heating a process medium (<NUM>), a current sensing arrangement (<NUM>), and a switching arrangement (<NUM>) configured to selectively couple a power supply (<NUM>) to the heating arrangement, the switching arrangement comprising at least one semiconductor switch (120A, 120B, 120C), the method comprising:
in response to a demand signal (<NUM>) for starting heating of the process medium, operating (<NUM>) the system in a test mode (<NUM>), wherein operating the system in the test mode includes performing a test sequence (230A, 230B) comprising:
controlling (232A, 232B) the switching arrangement to couple the power supply to the heating arrangement for a predetermined period;
monitoring (234A, 234B) an electric current through the heating arrangement during the predetermined period using the current sensing arrangement;
comparing (236A, 236B) the monitored electric current to an electric current threshold during the predetermined period; characterized by:
switching (<NUM>) the system from operation in the test mode to operation in a heating mode (<NUM>) if the monitored electric current remains below the electric current threshold for a duration of the predetermined period; and
switching (<NUM>) the system from operation in the test mode to operation in a dormant mode (<NUM>, <NUM>) if the monitored electric current meets or exceeds the electric current threshold during the predetermined period, wherein:
operation of the system in the heating mode includes controlling (<NUM>) the switching arrangement to couple the power supply to the heating arrangement for heating the process medium to achieve a target temperature and/or to maintain the process medium at the target temperature, and
operation of the system in the dormant mode includes controlling (<NUM>, <NUM>) the switching arrangement to decouple the power supply from the heating arrangement.