MONITORING APPLIANCE FOR DETECTING LEAKS OF A

REFRIGERANT FLUID FROM A SAFETY VALVE OF AN INDUSTRIAL REFRIGERATION SYSTEM. TECHNOLOGICAL BACKGROUND OF THE INVENTION

Field of application

The present invention relates in general to systems for detecting leaks of a refrigerant in industrial refrigeration systems. In particular, the invention relates to a monitoring appliance for detecting leaks of a refrigerant fluid, such as a refrigerant gas, from a refrigeration circuit, with particular reference to small leaks or seepages of pressurized refrigerant fluid from a safety valve of the refrigeration system.

Prior art

As is known, an industrial refrigeration system employing a pressurized refrigerant fluid comprises one or more safety valves. The function performed by a safety valve is that of protecting the system equipment, such as evaporator units, capacitors, liquid receivers, oil separators, displacement compressors, heat exchangers and simple pressure receivers, from possible conditions of overpressure which may be generated in the system itself with respect to the operating conditions for which such equipment was designed.

The safety valve opens when conditions are exceeded for which the valve was calibrated, i.e. when the thrust applied on the shutter by the pressurized fluid exceeds the force countering the spring acting on the shutter itself.

The most common safety valves ensure the repeatability of the intervention. This means that the initial calibrating conditions are automatically restored after a valve has intervened following an overpressure to protect the system equipment, i.e. after the same has opened and then closed again.

Nevertheless, manufacturers recommend replacing or servicing safety valves after they have intervened. Indeed, during the opening step, processing residuals of the components and the pipes may have accumulated on the valve gasket itself. Such effects may in the long run deteriorate or make the sealing of the valve defective upon reclosing. An incorrect sealing of the safety valve may cause small leaks of the pressurized refrigerant fluid or seepages from the system through the defective valve. Such small seepages of refrigerant constitute leaks of the refrigerant which are difficult to detect and although they are minimal, they may in the long run cause the emptying of the refrigeration circuit with subsequent economic, environmental damage and harm to the people operating in the vicinity of the refrigeration system. Moreover, an operator is often forced to inspect all the safety valves in the system to identify that on which such leaks are occurring, with subsequent waste of time and resource.

According to the system operating conditions and the type of refrigerant fluid used, once open, the safety valves may exhaust the refrigerant fluid directly into the surrounding environment or, in the cases in which there is the risk of causing direct harm to people in the vicinity, a pipe or duct is provided for conveying the exhausted refrigerant fluid which is sized so as not to jeopardize the operation of the valve itself. Generally, the safety standards for refrigeration systems recommend implementing each valve in the system with an exhaust pipe for the refrigerant fluid placed at the output or downstream of the valve itself.

Certain technical solutions for detecting the possible malfunctioning of a safety valve of a refrigeration system employed today aim to detect overpressure conditions to which the valve may be subjected. Among these solutions, burst discs are probably the most used system. This involves diaphragms placed upstream of the safety valve and calibrated to intervene by bursting following overpressures in the refrigeration circuit which are smaller than the overpressures which would cause the valve to open. When the pressure in the refrigeration circuit reaches the limit set for the intervention of the disc, such a disc bursts and a pressure transmitter (or a pressure switch) installed downstream of the disc sends an analog signal (or a digital contact) to the control system.

Therefore, the burst disc allows to detect the changes in pressure in the refrigeration circuit, thus signaling the risk that a leak of a refrigerant fluid may occur at a defective safety valve. However, such burst discs do not allow to detect an actual fluid leak because they do not provide information on the actual operating conditions of the valve.

Moreover, once they have intervened, burst discs cannot be used again and are to be replaced. Moreover, they are to be periodically inspected. In order to do this, there is a need for direct intervention on the refrigeration circuit, thus stopping the operability of the system.

SUMMARY OF THE INVENTION

It is the object of the present invention to devise and provide a monitoring appliance which allows to detect leaks of a refrigerant fluid from a refrigeration circuit, in particular the seepages of a refrigerant fluid from a safety valve of an industrial refrigeration system, thus at least partially overcoming the limits and drawbacks mentioned above in relation to the known solutions, for example the limits associated with the employment of burst discs.

Such an object is achieved by a monitoring appliance for detecting leaks of a refrigerant fluid, such as a refrigerant gas, from a refrigeration circuit of an industrial refrigeration system according to claim 1.

The invention relates to a monitoring appliance (100) for detecting leaks of a refrigerant fluid from a refrigeration circuit (150) of an industrial refrigeration system, which comprises: a body (1) having a first portion (2) for accommodating an electronic detection device (10) for detecting leaks of a refrigerant fluid, said first portion (2) being connected to an opposite second portion (3) of the body, said second portion (3) of the body comprises mechanical connection means (30) configured to connect the monitoring appliance to an exhaust pipe (60; 70) of the refrigerant fluid, associated with at least one safety valve (40; 50) of the refrigeration system, wherein said electronic detection device (10) comprises: - an optical oxygen sensor (11) adapted to detect a decrease in an oxygen level below a first and a second preset threshold value inside the exhaust pipe, from a reference oxygen level value, caused by a leak of a refrigerant fluid from the safety valve (40; 50) into the exhaust pipe (60; 70); an electronic control unit (12) connected to said optical oxygen sensor (11); an electronic status switching unit (13) which can be activated by the electronic control unit (12) to switch from a first (OFF) to a second (ON) status to signal the detection of a decrease in the oxygen level in the exhaust pipe (60, 70) below said first or second preset threshold value, exceeding said first threshold value identifies a leak of a refrigerant fluid from the safety valve (40; 50) which enables monitoring the valve, exceeding said second threshold value identifies a leak of a refrigerant fluid from the safety valve (40; 50) which enables a valve replacement operation. In particular, the invention provides a monitoring appliance for detecting leaks of a refrigerant, which is configured to be connected to an exhaust pipe of the refrigerant fluid associated with at least one safety valve of the refrigeration system and separate from the refrigeration circuit. Such an arrangement facilitates servicing the monitoring appliance because there is no need for interventions on such an appliance or the replacement of the same in order to intercept parts of refrigeration circuit or to create a vacuum in the system.

It is a further object of the invention to provide a monitoring appliance provided with mechanical means for the reversible connection to the exhaust pipe of the refrigerant fluid which facilitates and speeds up the installation operations of the monitoring appliance.

Preferred embodiments of such a monitoring appliance are described in the dependent claims.

The present invention also relates to a safety valve assembly for an industrial refrigeration system which includes the aforesaid monitoring appliance according to claim 13.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the monitoring appliance for detecting leaks of a refrigerant fluid according to the invention will become apparent from the following description of preferred embodiments thereof, given only by way of a non-limiting, indicative example, with reference to the accompanying drawings, in which:

Figure 1 diagrammatically shows an exploded view of a first embodiment of a safety valve assembly including the monitoring appliance for detecting leaks of a refrigerant fluid from the valve of the invention;

Figure 2 diagrammatically shows the safety valve assembly in Figure 1, in assembled configuration; - Figure 3 diagrammatically shows an exploded view of a second embodiment of a safety valve assembly including the monitoring appliance for detecting leaks of a refrigerant fluid from the valve of the invention;

Figure 4 diagrammatically shows the safety valve assembly in Figure 3, in assembled configuration;

Figure 5 shows a block diagram of an electronic device for detecting leaks of a refrigerant fluid included in the monitoring appliances in Figures 1 to 4. In the aforesaid figures, equal or similar elements will be indicated by the same reference numerals.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 1 to 4, a monitoring appliance for detecting leaks of a refrigerant fluid from a refrigeration circuit 150 of an industrial refrigeration system according to the present invention is indicated by reference numeral 100.

Such a monitoring appliance 100, hereinafter also simply appliance, particularly allows to detect small leaks of the pressurized refrigerant fluid or seepages of a refrigerant fluid from a safety valve 40, 50 of an industrial refrigeration system. Such a refrigerant fluid is for example a refrigerant gas, such as carbon dioxide, propane, freon, ammonia.

Additionally, the monitoring appliance 100 is also configured to detect the opening of the safety valve 40, 50 following an overpressure in the refrigeration circuit 150.

The monitoring appliance 100 comprises a body 1 having a first portion 2 for accommodating an electronic detection device 10 for detecting leaks of a refrigerant fluid. Such a first portion 2 of the body of the appliance is connected, in particular is connected in one piece, to an opposite second portion 3 of the body.

With reference to Figures 2 and 4, the second portion 3 of the body of appliance 100 comprises mechanical connection means 30 configured to connect the monitoring appliance 100 to an exhaust pipe 60, 70 of the refrigerant fluid, associated with at least one safety valve 40, 50 of the refrigeration system and separate from the refrigeration circuit 150. Moreover, the aforesaid electronic detection device

10 comprises an optical oxygen sensor 11 adapted to detect a decrease in an oxygen level in the exhaust pipe below at least one preset threshold value, caused by a leak of a refrigerant fluid in the exhaust pipe 60, 70.

The decrease, in particular percentage decrease, of the level of oxygen in the pipe is detected starting from a reference oxygen level value corresponding to a normal operating condition of the safety valve, i.e. in the absence of leaks.

In particular, the optical oxygen sensor 11 is adapted to detect a decrease in the oxygen level in the exhaust pipe 60, 70 below a first and a second preset threshold value, from a reference oxygen level value, caused by a leak of a refrigerant fluid from the safety valve 40, 50 into the exhaust pipe 60, 70.

Exceeding the first threshold value identifies a leak of a refrigerant fluid from the safety valve 40, 50 which enables monitoring the valve. Exceeding the second threshold value identifies a leak of a refrigerant fluid from the safety valve 40, 50 which enables a valve replacement operation.

In an embodiment, the electronic detection device 10 for detecting leaks of a refrigerant fluid materializes in a printed circuit board (PCB). The optical oxygen sensor 11 is mounted on such a circuit board 10.

For example, such a first threshold value identifies a percentage decrease in the oxygen in pipe 60, 70 caused by a small leak or seepage of a refrigerant fluid, for example a fluid leak of 5% in volume (Warning) in the pipe. Once signaled, this small leak generally does not require intervention on valve 40, 50 if it is sporadic. Moreover, such a second threshold value identifies a significant percentage decrease in the oxygen in the pipe 60, 70 caused by a considerable leak of a refrigerant fluid or by seepage which continues over the long run, in the pipe through a defective valve, for example a fluid leak of 15% in volume (Alarm) in the pipe. Exceeding such a second threshold value is indicative of a defect in the sealing of the safety valve 40, 50 which requires servicing or replacing valve 40, 50 itself to prevent the emptying of the refrigeration circuit 150. The present invention allows to define a first and a second threshold value, allowing to discriminate between a decrease in oxygen caused by simple seepage of the safety valve (first threshold) and a decrease in oxygen in the exhaust pipe caused by a significant leak of a refrigerant fluid (second threshold). This ensures increased efficiency and reliability of the monitoring appliance 100 which allows to discriminate the operating conditions of the valve not requiring a replacement operation of the valve itself from those requiring such a replacement due to the defectiveness of the safety valve.

The fact that the monitoring appliance 100 of the invention detects the leaks of a refrigerant gas through an analysis by "subtraction" makes it adapted to installation in systems operating with any type of a refrigerant gas, in addition to those indicated above. Such gases also comprise potentially explosive gases with which only products conforming with the ATEX (ATmosphere Explosible) standard may be used. In particular, the ATEX standard groups together all the electrical/electronic and mechanical appliances and the protection devices found in environments at the risk of explosion.

For example, the optical oxygen sensor 11 consists of a florescent optical sensor, such as the compact oxygen sensor indicated by the trade name Lumin0x02 by SST Sensing Ltd., operating with a supply voltage of 4.5V-5.5V, in a range of temperatures from -30°C to +60°C, provided with a TTL (transistor-transistor logic) digital output and response time under 30 msec. In this embodiment, the aforesaid mechanical connection means 30 of the appliance configured to connect the monitoring appliance 100 to the exhaust pipe 60, 70 of the refrigerant fluid are mechanical connection means of reversible type. In greater detail, such reversible mechanical connection means consist of a push-in connector 30 with threaded coupling associated with the connection portion 3 of the monitoring appliance 100. For example, such a threaded coupling is a 1" coupling. In a more general embodiment which may be described with reference to Figure 5, in addition to the optical oxygen sensor 11, the electronic detection device 10 for detecting leaks of a refrigerant fluid comprises: an electronic control unit 12 connected to such an optical oxygen sensor 11 for receiving a digital voltage signal representative of a level or amount of oxygen detected in the exhaust pipe 60, 70; an electronic status switching unit 13 which can be activated by the electronic control unit 12 to switch from a first (OFF) to a second (ON) status to signal the detection of a (percentage) decrease in the oxygen level in the exhaust pipe 60, 70 below at least one preset threshold value, for example the first threshold value or the second threshold value mentioned above. In particular, the electronic control unit 12 comprises a microcontroller, for example 8 bits operating at 8 MHz, equipped with a respective storage, for example of the volatile type, for storing data, and possibly with a system storage of non-volatile type (for example of EEPROM type).

Both the electronic control unit 12 and the optical oxygen sensor 11 are supplied, for example at a voltage of 5V, by a direct current (DC) voltage supply block 18 starting from an input voltage V _IN of 24V (minimum 12V - maximum 30V). The voltage supply to the electronic components of the detection device 10 is signaled by the activation of a respective light signal 19, for example a green LED turns ON.

In order to be adapted to installation on refrigeration circuits operating with potentially explosive gases, the monitoring appliance 100 of the invention comprises suitable over-current, short-circuit, overvoltage and electrostatic discharge protections. Such protections allow the optical oxygen sensor 11 to operate in contact with such gases despite it not originally being adequate for this function.

In particular, the monitoring appliance 100 comprises a first fuse, such as a 200mA fuse, of the resettable type, connected in series to the power supply of the circuit board 10 to limit the current in case of short circuits in the power supply. In particular, such a first fuse is connected between the input voltage terminal V _IN and the voltage supply block 18 of the electronic detection device 10. Moreover, the monitoring appliance 100 comprises a first resistance, such as a 22W resistance, connected between the electronic control unit 12 and the optical oxygen sensor 11 to limit the current to the oxygen sensor 11 in case of a short circuit of the latter. Additionally, to prevent the superheating of such a first resistance, the monitoring appliance 100 comprises a second fuse, such as a 125mA fuse, connected on the output line of the voltage supply block 18.

It should be noted that the value of such a first resistance is selected to have a maximum drop of 500 mV thereon so as to provide the optical oxygen sensor 11 with at least a 4.5V supply voltage, which is the minimum voltage for correct operation. Indeed, by selecting such a first resistance equal to 22W, the currents involved in the monitoring appliance 100 cause a maximum drop in voltage on such a first resistance of about 440 mV.

Therefore, in the worst case, the supply voltage of the oxygen sensor 11 is equal to about 5V - 0.44V = 4.56V.

Additionally, the monitoring appliance 100 comprises a second and a third resistance, for example equal to each other and having value of 330W, connected in series on the signal communication line connecting the electronic control unit 12 and the oxygen sensor 11. Such second and third resistances further protect PCB 10 and the optical oxygen sensor 11 in case of malfunctioning.

It should be noted that the electronic status switching unit 13 of the electronic detection device 10 is selected from the group consisting of:

- an electromechanical relay, for example including three contacts (NO - C - NC) or only 2 contacts (NO - C);

- a P-channel power MOSFET transistor;

- an N-channel power MOSFET transistor;

- a solid state relay.

At the discretion of the user and always while respecting the technical features of the device, the electronic switching unit 13 implemented with relays may be interfaced with a control system (PLC, controllers, and the like) in which a logic for generating signals and/or alarms may be implemented upon switching the relay.

In the more general embodiment, the electronic detection device 10 further comprises a data communication unit 14 connected to the electronic control unit 12, for sending, out from the monitoring appliance 100, data representative of the performed detections of leaks of a refrigerant gas and for receiving, in the monitoring appliance 100, configuration instructions for operating parameters of the optical oxygen sensor 11.

In particular, such a data communication unit 14 is a fieldbus line operating according to a communication protocol selected from the group consisting of: Modbus RTU, Modbus TCP, Profinet, Profibus, CAN bus.

In a different embodiment of the monitoring appliance 100 of the invention, the electronic detection device 10 may also comprise an analog current output unit 15, for example 4-20 mA, configured to connect the monitoring appliance 100 to an external control system.

For example, such an external control system may comprise electronic controllers, PLCs (Programmable Logic Controllers) or third-party devices capable of executing any alarm procedures.

In a different embodiment of the monitoring appliance 100 of the invention, the electronic detection device 10 may also comprise an analog voltage output unit 16 alternatively to the analog current output 15. Such a voltage output 16, for example of 0-10V, is configured to connect the monitoring appliance 100 to the above- mentioned external control system.

In a different embodiment again of the monitoring appliance 100 of the invention shown in Figure 5, the electronic detection device 10 may comprise both an analog voltage output unit 16 and an analog current output unit 15, both enclosed in the dotted block 21.

To protect from any short-circuit loads, the monitoring appliance 100 of the invention comprises third resettable fuses, such as 50 mA fuses, operatively associated with the analog voltage output unit 16 and the analog current output unit 15.

Again, to protect from any short-circuit loads, the monitoring appliance 100 also comprises fourth resettable fuses, such as 200 mA fuses, operatively associated with the data communication unit 14.

Moreover, the monitoring appliance 100 comprises two-way TVS diodes, such as 1.5kW diodes, for limiting any over-voltages, and Schottky diodes for limiting any electrostatic discharges and polarity reversals. Such diodes are associated with blocks 18, 13, 14, 15 and 16 in Figure 5 to protect the input signals, the output and supply signals of the monitoring appliance 100 from the aforesaid over-voltages or electrostatic discharges.

Since it comprises all the above-mentioned protections, the monitoring appliance 100 of the invention meets the requirements required by the ATEX standard and may be employed in environments at the risk of explosion. Moreover, a bi-component resin adapted to cover and incorporate the circuit board 10 inserted into body 1 is employed to manufacture the monitoring appliance 100. Such a resin is selected from resins having features of resistance to heat and to atmospheric and chemical deterioration which allow to protect the circuit board 10. With such a resin, the circuit board 10 is not affected by external heat sources up to a temperature of 135°C. Moreover, the resin protects the components of the circuit board 10 also in case of a breakdown or malfunction of one of them, thus ensuring one of the requirements required by the ATEX standard.

Moreover, in all the above-mentioned examples, the electronic detection device 10 comprises visual signaling means 17 of an alarm which can be activated by the electronic control unit 12 following the detection of a decrease in the level of oxygen in pipe 60, 70 below the preset threshold value, i.e. upon the detection of a leak of a refrigerant fluid which is greater than a respective first threshold (Warning) or greater than a respective second threshold (Alarm). Such visual signaling means 17 consist of an orange LED, which turns ON to signal the first threshold value (Warning) has been exceeded, and a red LED, which turns ON to signal the second threshold value (Alarm) has been exceeded. With reference to Figures 1 to 4, a safety valve assembly 200, 300 of an industrial refrigeration system is described below. Such an assembly comprises:

- a safety valve 40, 50 having a respective inlet 41, 51 connected to a refrigeration circuit 150 of the industrial refrigeration system, and an outlet 42, 52 connected to an exhaust pipe 60, 70 of the refrigerant fluid;

- a monitoring appliance 100 for detecting leaks of a refrigerant fluid of the above-described present invention;

- first reversible mechanical connection means 61, 62, 71 associated with a first end 43, 53 of the exhaust pipe

60, 70 of the refrigerant fluid adapted to reversibly engage the aforesaid outlet 42, 52 of the safety valve

40, 50;

- second reversible mechanical connection means 63, 64,

72 associated with a second end 44, 54 of the exhaust pipe 60, 70 of the refrigerant fluid adapted to reversibly engage connection means 30 of the monitoring appliance 100.

With reference to the example of safety valve assembly 200 of an industrial refrigeration system in Figures 1 to 2: - the first reversible mechanical connection means 61, 62 associated with the first end 43 of the exhaust pipe 60 of the refrigerant fluid comprise a first 61 and a second 62 push-in connector with threaded coupling;

- said second reversible mechanical connection means 63, 64 associated with the second end 44 of the exhaust pipe of the refrigerant fluid comprise a third 63 and a fourth 64 push-in connector with threaded coupling.

With reference to the example of safety valve assembly 300 of an industrial refrigeration system in Figures 3 to 4: the first reversible mechanical connection means 71 associated with the first end 53 of the exhaust pipe 70 of the refrigerant fluid comprise a push-in connector with flanged coupling; - the second reversible mechanical connection means 72 associated with the second end 54 of the exhaust pipe 70 of the refrigerant fluid comprise a push-in connector with threaded coupling.

From an operational viewpoint, the monitoring appliance 100 allows to monitor the percentage value of the amount of refrigerant gas in an exhaust pipe 60, 70 of the refrigerant fluid associated with one or more safety valves 40, 50 of the system by monitoring the percentage value of the oxygen levels in such an exhaust pipe. In other words, a decrease in the oxygen in the exhaust pipe 60, 70 below the above-mentioned first threshold value from a reference oxygen level is indicated by appliance 100 as an increase in percentage value above a respective first threshold value of the amount of refrigerant gas in the same pipe of the refrigerant gas, or warning threshold (Warning) of the amount of refrigerant gas.

Moreover, a decrease in the oxygen in the exhaust pipe 60, 70 below the above-mentioned second threshold value from a reference oxygen level is indicated by appliance 100 as an increase in percentage value above a respective second threshold value of the amount of refrigerant gas in the same pipe of the refrigerant gas, or alarm threshold (Alarm) of the amount of refrigerant gas.

Following the detection by the optical oxygen sensor 11 of a decrease in the percentage level of oxygen in pipe 60, 70 from a reference level under normal conditions, such as to bring the percentage level of the amount of refrigerant gas above the respective first preset threshold value, for example the warning threshold value (Warning), or above the respective second preset threshold value, for example the alarm threshold value (Alarm), the monitoring appliance 100 is configured to signal, through the electronic control unit 12, the warning or alarm conditions and to locally activate the visual signaling 17 and simultaneously the electronic status switching unit 13.

Moreover, by means of the data communication unit 14 operating for example according to the MODBUS protocol, with which the monitoring appliance 100 is equipped, the values related to the percentage value of the amount of refrigerant gas detected in the exhaust pipe associated with valve 40, 50 may be read and the values related to the respective first percentage warning threshold value of refrigerant gas and the respective second alarm percentage threshold value of refrigerant gas may be written and changed in the monitoring appliance 100. Moreover, the monitoring appliance 100 is also configured to detect the atmospheric pressure and the temperature of the environment. The value of this environmental data is written in specific Modbus registers. In startup step (Startup), the LuminOx 02 sensor employed in appliance 100 requires at least 30 seconds to reach normal running. Such a startup time may be changed by means of a specific Modbus register. The set reference parameter generally is 40 seconds. The monitoring appliance 100 updates the current and voltage output with a value which is proportional to the percentage amount of refrigerant gas measured both over the startup period and during the regular operation.

Once startup is complete, the device may signal the presence of a possible alarm or warning.

With reference to the voltage and current outputs 15, 16 described above, it should be noted that: the 0V DC output is representative of a 0% change in the amount of refrigerant gas detected; - the 10V DC output is representative of a 100% change in the amount of refrigerant gas detected; the 4mA output is representative of a 0% change in the amount of refrigerant gas detected; the 20mA output is representative of a 100% change in the amount of refrigerant gas detected.

The switching unit 13 is configured by means of Modbus register, in particular in case of a relay. For example, the response configuration of relay 13 to an alarm is detailed below: STARTUP: N.O. contact not switched,

OK STATUS: N.O. contact not switched,

WARNING STATUS: N.O. contact not switched,

ALARM STATUS: RELAY_ALARM_ENABLED= 1 -> N.O. contact switched, RELAY ALARM ENABLED= 0 -> N.O. contact not switched. The following are certain parametrization registers of the monitoring appliance 100. In particular, the register - CURRENT_GAS: indicates the instantaneous gas value (%). The oxygen sensor 11 measures a percentage of oxygen in the range [0 - 25] % and the formula for measuring the gas in the pipe 60, 70 is:

GAS= (OXYGEN_SET_POINT - "instantaneous oxygen")*(100/ OXYGEN_SET_POINT) where OXYGEN_SET_POINT is a parameter representative of a reference value of the level of oxygen in the pipe and "instantaneous oxygen" is a variable representative of the measurement taken through sensor 11.

Other parametrization registers of the monitoring appliance 100 comprise: - CURRENT_TEMPERATURE: instantaneous temperature value (°C);

CURRENT_PRESSURE: instantaneous pressure value

(mbar);

- GAS_SET_POINT: The setpoint register is configured by the device once startup is complete.

The GAS_SET_POINT register may only be read in Modbus.

The register is updated also after the startup and only if the value CURRENT_OXYGEN > OXYGEN_SET_POINT; - GAS_DELTA_WARNING: percentage of change of the GAS with respect to GAS_SET_POINT which may generate a Warning signal;

CURRENT_GAS < (GAS_SET_POINT + GAS_DELTA_WARNING) -> OK,

CURRENTJGAS > (GAS_SET_POINT + GAS_DELTA_WARNING)-> Warning signal,

GAS_DELTA_ALARM : percentage of change of the GAS with respect to GAS_SET_POINT which may generate an Alarm signal,

CURRENTJGAS < (GAS 3ET_P0INT + GAS_DELTA_ALARM)->

OK,

CURRENT GAS > (GASJ3ET_P0INT + GAS_DELTA_ALARM) -> Alarm signal,

GASJ3TARTUP_ALARM : threshold value used to generate an alarm at the end of the startup step if: GAS_SET_POINT >= GAS_STARTUP_ALARM

This alarm cannot be cancelled; it is permanent. The device requires restarting to remove the alarm;

STARTUPJTIME: this register specifies the duration of the startup step; during this initial step, appliance 100 does not generate any warnings or alarms;

RELAY_ALARM_ENABLED: relay signaling enabling 0 -> relay disabled in case of an alarm,

1 -> relay enabled in case of an alarm; ALARM_DETECTED: this register signals if the device has identified an alarm condition (register set to l); even if the device were to leave the alarm condition, the "flag" signaling of this register remains at 1.

Cancellation of the alarm: Modbus coding of 0 allows to reset the register status.

EXAMPLE The Applicant has performed operating tests of the monitoring appliance 100 of the invention associated with a safety valve calibrated at a pressure of 20 bar, having an exhaust pipe with a diameter of 2.1/2" (DN65) installed in a system which employs carbon dioxide (C02) as refrigerant fluid. The seepage or opening of the valve may be monitored through appliance 100 by defining the following parameters.

1) Reference value for the type of fluid, the calibration pressure, and the dimensions of the safety valve, e.g. 416 grams of refrigerant leak per percentage point per minute, as per laboratory tests and indicated in Table 1 (values obtained in a laboratory at 25°C and 1013 mbar with approximation of +/- 10%). TABLE 1

2) Carbon dioxide system with total load of 8000 kg, where the end user has set the following threshold values for the refrigerant fluid leak (in percentage) from the valve:

- Warning threshold set by the user 20%;

- Alarm threshold set by the user 25%.

For refrigerant fluid leaks from the valve between 0 grams (0%) and 7904 grams (19%), the monitoring appliance 100 displays the leak percentage through the prepared outlets.

For refrigerant fluid leaks from the valve from 8320 grams (20%) up to 9984 grams (24%), the monitoring appliance 100 signals, through visual signaling and prepared outlets, a Warning status to warn of an occurrence which requires attention by appointed personnel.

For refrigerant fluid leaks from the valve greater than 10400 grams (25%), the monitoring appliance 100 signals the Alarm status, through visual signaling and possibly closing the Alarm relay, and where combined with a remote-monitoring system, sends an e-mail that an alarm has been triggered.

It should be noted that the user may program the thresholds according to the dimension of the monitored safety valve, the calibration pressure, the type of refrigerant fluid used and the position in which the monitoring appliance 100 is installed in the system.

The monitoring appliance 100 of the invention provides the advantage of promptly intervening if a safety valve 40, 50 opens or seeps so as to avoid dispersions of refrigerant gas into the environment, possible system stops, and to contribute to ensuring increased safety for the people who are in the vicinity of the system itself.

The monitoring appliance 100 also ensures installation and maintenance advantages. Indeed, by virtue of the 1" threaded coupling with which it is provided, appliance 100 may be easily installed on the conveying pipes of the exhausts of the safety valves 40,

50 of a system. Moreover, since it is installed downstream of the safety valve, appliance 100 is outside the refrigeration circuit 150, thus facilitating installation and possible maintenance operations because there is no need to either intercept parts of the circuit or to create a vacuum in the system.

As is known by those skilled in the art, appliance 100 always operates at room temperature and at a standard atmospheric pressure outside of the refrigeration circuit 150, independently of the system operating conditions.

Moreover, the value of oxygen in the environment is always about 20.95% of the air mixture. This allows to use a single sensor for all the types of systems because, in case of a refrigerant gas leak, there will be a decrease in the percentage of oxygen regardless of the refrigerant gas used.

The monitoring appliance 100 of the invention also ensures detection accuracy and speed. As already mentioned, after the valve has intervened in the most common safety valves, i.e. it has opened and closed again to compensate for an overpressure, ensuring the complete restoration of the initial calibration condition of the valve itself is not possible.

An imperfect sealing of the valve may cause leaks of a refrigerant fluid into the environment which might not be identified by the fixed safety detectors installed in the system because such leaks often are insufficient to saturate the environment in which the refrigeration unit is located, but may empty the refrigeration circuit in the long run. Contrarily, the monitoring appliance 100 of the invention is configured to also detect small leaks or seepages of a refrigerant fluid resulting from the malfunctioning of a safety valve which has already intervened. Indeed, the amount of air in the exhaust pipe 60, 70 installed downstream of the safety valve 40, 50 requires a small gas leak to saturate or reduce the percentage level of oxygen therein, with the consequence that the leak is detected in a short period of time. Moreover, since appliance 100 is installed at the output of one or a small group of safety valves, the area of the person requiring intervention by the maintenance operator may be identified.

Those skilled in the art may make changes and adaptations to the embodiments of the monitoring appliance of the invention or may replace elements with others which are functionally equivalent, in order to meet contingent needs without departing from the scope of the following claims. Each of the features described as belonging to a possible embodiment can be achieved irrespective of the other embodiments described. kkk k kkk