A resistive temperature device, misalignment sensor, conveyor system and method for measuring misalignment of a conveyor system

The invention relates to a resistive temperature device, a misalignment sensor including such a resistive temperature device, a conveyor system including a misalignment sensor, and a method for measuring misalignment of a conveyor system. In the bulk handling industry, use is often made of conveyor systems in which bulk material is transported from one location to another. Especially in case of dry bulk material there is the risk of a dust explosion during handling of the bulk material.

A dust explosion occurs when:

- there is a combustible dust,

- the dust is suspended in the air at a high concentration,

- there is an oxidant, e.g. oxygen, and

- there is an ignition source. Examples of ignition sources are an electrostatic discharge or a hot surface which both may be produced by friction of elements moving relative to each other as often encountered in conveyor systems.

One approach to prevent a dust explosion is to prevent the occurrence of an ignition source which requires an appropriate design of the conveyor systems used in the bulk handling industry. The importance of this is also recognized by the European Commission which issued a Directive 94/4/EC also known as the ATEX Guidelines to set a safety standard for use of equipment in potentially explosive atmospheres. A source of ignition may be formed in conveyor systems when misalignment of a conveyor belt occurs which causes frictional contact between the moving conveyor belt and another component of the conveyor system, usually a stationary component part of the conveyor belt carrying structure. This frictional contact may generate heat and thus an increase of temperature of components of the conveyor system. Typically, temperatures above 80 degrees Celsius are reached during such frictional contact, so that the heated component is a potential ignition source. It is therefore desirable to detect misalignment of conveyor belts. The detectors which are able to detect misalignment of the conveyor belts will be called misalignment sensors in this application from now on. Three types of misalignment sensors are already available on the market. These types include:

an inductive type;

a capacitive type; and

a contact switch type. The inductive type misalignment sensor measures the position of the conveyor belt by measuring the inductance and thus interacts with iron parts in the conveyor belt or parts carried by the conveyor belt. However, this type of sensor is for instance not suitable when only plastic parts are used. A capacitive type misalignment sensor measures the position of the conveyor belt by measuring the capacitance. However, pollution of the sensor may cause disturbances which renders the sensor less accurate.

A contact switch type misalignment sensor is able to detect misalignment of the conveyor belt by sufficient contact between sensor and conveyor belt such that a switch is triggered. A disadvantage of this type is that it only detects if the misalignment reaches a predetermined value and thus simply acts as a yes/no switch.

It is therefore an object of the invention to provide an improved misalignment sensor which can be used with any kind of material, is minimally effected by dust and pollution and provides more information than a simple yes/no answer to the question if the misalignment has reached a predetermined value or not.

The invention achieves this object by providing a method for measuring misalignment of a conveyor belt in a conveyor system with the following steps:

• providing a thermally isolated engagement surface for frictional contact between engagement surface and the conveyor belt in case of misalignment of the conveyor belt;

• monitoring the temperature of the engagement surface; and

· determining misalignment of the conveyor belt from the monitored temperature of the engagement surface. The method advantageously uses the heating effect of frictional contact that naturally occurs during misalignment. This heating effect takes place for a wide variety of materials, thereby making this measuring method in principle independent of the materials used for the engagement surface and the conveyor belt as most combinations of materials will result in heating of the engagement surface.

By thermally isolating the engagement surface it is prevented that heat is transferred to other parts of the conveyor system which allows to measure the temperature effects of relatively small amounts of generated heat, i.e. minimal frictional contact between engagement surface and conveyor belt can be detected.

The method has the additional advantage that dust and pollution that have accumulated on the engagement surface are automatically removed by the frictional contact, so that the measurement can be performed substantially independent of dust and pollution.

Further, more information than a yes/no answer to the question whether misalignment has occurred to a certain extent or not can be obtained as the temperature of the engagement surface indicates the extent of misalignment and also indicates whether the misalignment may result in becoming an ignition source. The method thus can be used in a feedback loop in which the misalignment is measured and appropriate action, e.g. pivoting conveyor belt carrying elements to counteract the misalignment, can be taken.

Another advantage may be that when frictional contact is absent between the engagement surface and conveyor belt, the method outputs a constant ambient temperature reading signal which is an indication that the system or device carrying out the method is operative and in stand-by mode. This is different from the prior art misalignment sensors as they usually only output a signal in case of misalignment. As a result, using the method according to the invention a potentially hazardous situation due to a failing system or device carrying out the misalignment measuring method can be prevented as the failing of said system or device can be detected.

As an example of using the method according to the invention, misalignment of the conveyor belt will result in a raise of temperature of the engagement surface due to frictional contact. The temperature may raise until a first danger level is reached. This danger level may indicate that the supply of bulk material should be stopped while the conveyor system itself keeps on running. In this way the concentration of bulk material is lowered in order to avoid a hazardous situation. If the misalignment is not corrected for in time, a second danger level of the temperature may be reached, which may require to shut down the conveyor system in order to stop the heating by frictional contact to minimize the risk of a dust explosion and possibly investigate why the misalignment continued to be present despite other measures that were taken.

In order to carry out the abovementioned method, the invention also provides a

misalignment sensor comprising:

- a mounting part to mount the sensor to a stationary part of a conveyor system; - a friction part with an engagement surface for frictional contact with a conveyor belt of the conveyor system during misalignment of the conveyor belt;

- thermal isolation between friction part and mounting part; and

- a temperature device to measure the temperature of the friction part, wherein said temperature device is preferably extending through the mounting part and the thermal isolation.

In an embodiment, the thermal isolation is provided by a rubber part or a part made of Teflon, e.g. high heat Teflon which has the additional advantage that it is FDA approved. A typical thickness of the thermal isolation is about 12 mm.

The mounting part, friction part and the thermal isolation may together form a sandwich structure.

In an embodiment, the mounting part, friction part and the thermal isolation are attached to each other using an appropriate adhesive. Additionally or alternatively the mounting part, friction part and the thermal isolation may be clamped together by bolt-nut combinations. In order to avoid heat leakage via the bolt-nut combinations, a thermal isolating bushing may be provided around the bolt-nut combination. If thermal isolation is not possible or difficult to implement, it is preferred to provide good thermal contact between the bolt-nut combination and the mounting part in order to avoid the ends of the bolt-nut combination from becoming too hot and potentially become an ignition source. Due to the good thermal contact, heat can easily spread across the mounting part with a lower temperature as a result.

In an embodiment, heat transfer from friction part to mounting part while attaching them properly together is avoided by providing a connection element, e.g. a bolt or screw, between the mounting part and the thermal isolation that is separate from a connection element between the friction part and the thermal isolation. The thermal isolation may therefore be provided with respective separate threaded holes to receive a bolt or screw in order to attach both the friction part and mounting part to the thermal isolation

In an embodiment, the size of the friction part is a compromise between being large enough to allow frictional contact between friction part and conveyor belt in case of misalignment and small enough to have a small heat capacity as a result of which the response time of the sensor is short enough. The size may further be determined by the available space and mounting requirements. Preferably a circular shaped engagement surface is provided, but other shapes are also possible, for instance rectangular shaped engagement surfaces.

In an embodiment, the temperature device extends through the mounting part, thermal isolation and possibly the friction part using a form fit which not only fixes the temperature device relative to the misalignment sensor but also provides sufficient thermal contact between friction part and misalignment sensor.

The misalignment sensor can be used to detect the heat generated by frictional contact between the friction part and a moving conveyor belt to measure the misalignment of the conveyor belt, but the misalignment sensor can also be used to measure misalignment of other components of the conveyor system such as a conveyor belt carrying element. The always present signal of the temperature reading due to the at least detected ambient temperature allows to monitor this misalignment. In case for instance a conveyor belt carrying element fails and goes off track, the temperature reading may be disrupted, e.g. by damage to the misalignment sensor as a result of contact between the conveyor belt carrying element and the misalignment, thereby indicating the misalignment of the conveyor belt carrying element. The invention thus also relates to a misalignment sensor comprising:

- a mounting part to mount the sensor to a stationary part of a conveyor system;

- a friction part for contact with the conveyor system during misalignment of the conveyor system;

- thermal isolation between friction part and mounting part; and

- a temperature device to measure the temperature of the friction part, wherein said temperature device extends through the mounting part, thermal isolation and friction part to be contacted by the conveyor system in case of misalignment of the conveyor system.

As heat may be an ignition source for dust explosions it is important to accurately measure the temperature of the friction part without introducing new possible ignition sources.

Therefore the temperature device is preferably a resistive temperature device comprising: - an elongated container having a closed distal end and a proximal end;

- a thermistor positioned inside the container near the distal end;

- connection leads connected to the thermistor and extending from the thermistor to the proximal end to connect the thermistor to a measuring device;

- thermal grease arranged between the thermistor and the distal end of the

container; and

- thermally isolating material arranged inside the container between the thermal grease and the proximal end of the container to provide a thermal insulation between distal end and proximal end of the container.

The elongated container allows to easily arrange the temperature device such that it extends through the mounting part and the thermal isolation of the misalignment sensor, preferably using a form fit. The thermistor allows a simple measurement principle while providing high accuracy and repeatability. The thermal grease has the advantage that a good contact between thermistor and container can be obtained so that heat can easily be transferred from the friction part to the thermistor via the surrounding walls of the container. The thermally isolating material in combination with the elongated contained increases the thermal resistance between distal end and proximal end of the resistive temperature device thereby providing the advantages that the temperature of the friction part itself is not too much influenced by the measurement device, that the response time of the temperature device decreases, and that other parts of the temperature device, e.g. parts exposed to an environment where dust can be present in dangerous concentrations, do not become a possible ignition source.

In an embodiment, the elongated container has relatively thin walls as this has two advantages: 1 ) it minimizes the thermal resistance in thickness direction which allows an easy heat transfer at the distal end to the thermistor, and 2) it increases the thermal resistance in longitudinal direction of the temperature device, thereby improving the thermal isolation between the distal end and proximal end.

In an embodiment, the thermistor is a platinum element which yields a more or less linear relationship between electrical resistance of the element and the temperature with respect to usually used NTC (negative temperature coefficient) and PTC (positive temperature coefficient) materials. Platinum further allows a large measurement range. Resistive temperature devices using platinum elements are often referred to as PTxxx elements or sensors, where PT stands for platinum and the xxx indicates the electrical resistance in Ohms at zero degrees Celsius. A resistive temperature device having a platinum element that has an electrical resistance of 100 Ohms at zero degrees Celsius may thus alternatively be referred to as a PT100 element or sensor.

The electrical resistance as a function of temperature is subject to some standards such as DIN 43760 (1980), IEC751 (1983) and BS1904 (1984). For instance, the resistance for a PT100 as a function of temperature can be described as:

R=100+0.385055xT or

R=100+0.390802xT-0.0000580195xT ² ,

where R is the electrical resistance of the platinum thermistor in Ohms and T is the temperature in degrees Celsius. In an embodiment, the thermally isolating material is also electrically isolating to provide electrical isolation between the connection leads themselves and between a connection lead and the wall of the elongated container which may be made of an electrically conductive material to shield the connection leads from external influences. An example of a class of materials that is both thermally and electrically isolating is an inorganic mineral powder or mineral isolated powder coating.

In an embodiment, the resistive temperature device also extends through the friction part in order to get a proper thermal contact between friction part and temperature device. The thermistor is then preferably located in the portion of the container extending through the friction part. Preferably, the distal end of the container of the resistive temperature device lies flush with the engagement surface of the friction part. As a result, there may be frictional contact between the distal end of the temperature device and the conveyor belt which provides an effective transfer of heat to the temperature device.

An important design aspect of the misalignment sensor is the chosen materials and their hardness which have an impact on the acceptance of the misalignment sensor in view of the ATEX Guidelines or other requirements. A relatively soft material will wear too much, but a relatively hard material may crumble due to the friction forces. Crumbling of parts is to be avoided especially when the sensor is used in a conveyor system handling bulk food materials. The friction part is therefore preferably made of brass in particular CuZn37 HH which is found to give the best results in view of heat conductivity and wear-resistance. The result may be that the friction part is still suspected to wear. When the distal end of the resistive temperature device initially lies flush with the engagement surface, but the position of the engagement surface changes due to wear, the loads on the temperature device may become too much. The distal end of the temperature device is therefore preferably of the same material as the friction part so that the wear ratios are equal. The distal end then preferably also has a wear portion to protect the thermistor in the container. The wear portion is made of solid material and has a thickness which is significantly larger than the wall thickness of the container and which may in practice be in the order of 1 -5mm, preferably 2-2.5mm.

In an embodiment, the thermal grease is only located in the portion of the container that extends through the friction part in order to efficiently transfer heat from the friction part to the thermistor without creating a too large thermal leak to the mounting part via the temperature device.

An advantage of the resistive temperature device extending through the friction part is that it may be possible to detect failure of conveyor belt carrying elements as well. For instance, a conveyor belt may be supported by a rotatable drum or roller. The rotatable drum is kept in place by appropriate bearings. However, occasionally, the bearings may fail as a result of which the rotatable drum may abruptly be moved sideways. The misalignment sensor is then preferably positioned such that this abrupt movement will result in a collision between the misalignment sensor and the drum such that the friction part and the portion of the temperature device extending through the friction part are separated from the misalignment sensor. This occurrence can be measured as the thermistor is now separated from its connection leads resulting in the measurement of a sudden infinite electrical resistance. The conveyor system can then be stopped in time to prevent further damage.

In an embodiment, the mounting part is made of stainless-steel.

In an embodiment, the connection elements attaching the friction part and mounting part respectively to the thermal isolation part are preferably made of the same material as the friction part and mounting part. Hence, in case of a brass friction part and a stainless-steel mounting part, the bolts or screws connecting the friction part to the thermal isolating part are also made of brass and the bolts or screws connecting the mounting part to the thermal isolating part are also made of stainless-steel. The invention also relates to a conveyor system including one or more of the abovementioned aspects of the invention.

The conveyor system minimally requires an endless conveyor belt, a conveyor belt carrying element, e.g. rotatable drum, for carrying the endless conveyor belt, and at least one misalignment sensor according to the invention to measure misalignment of the conveyor belt.

As misalignment can occur at both conveyor belt carrying elements and in two directions, it is preferred to provide two misalignment sensors at the conveyor belt carrying element, wherein one misalignment sensor detects the misalignment in one direction and the other misalignment sensor detects the misalignment in the other direction.

The invention will now be described in a non-limiting way with reference to the drawings, in which like parts are indicated by like reference numerals, and in which:

Fig. 1 depicts in schematic cross-sectional view a resistive temperature device according to an embodiment of the invention;

Fig. 2 depicts in partial view a schematic cross-sectional view of a resistive temperature device according to another embodiment of the invention;

Fig. 3A depicts schematically a misalignment sensor in front view according to an embodiment of the invention;

Fig. 3B depicts a cross-section of the misalignment sensor of Fig 3A;

Fig. 4 depicts a cross-section of a misalignment sensor according to a further embodiment of the invention;

Fig. 5 depicts a front view of a misalignment sensor according to yet another embodiment of the invention; and

Fig. 6 depicts partially in schematic view a conveyor system according to an embodiment of the invention. Fig. 1 depicts in schematic cross-sectional view a resistive temperature device RTD according to an embodiment of the invention. The resistive temperature device RTD comprises an elongated container EC, which in this case is a thin-walled cylindrically shaped container. Elongated in this context means that the length L of the container is significantly larger than the diameter D of the container, in particular the length L is at least 5 times the diameter D, preferably at least 10 times the diameter D. The container EC has a closed distal end DE and a proximal end PE. The proximal end PE of the container EC does not necessarily have to be an open end, but it may contain openings for connection leads or a connector as will be explained below.

The diameter D of the container may be in the order of 3-5 mm. It it noted here that it is not necessary to have a constant diameter. The container may therefore comprise portions having different diameters. The container itself may be mountable to other elements, for instance an element that carries an amplifier circuit and/or can be used to mount the container to other parts. Inside the elongated container EC, a thermistor TH is positioned near the distal end DE. The thermistor TH has an electrical resistance which is dependent on the temperature of the thermistor TH and can thus be used as a temperature sensor by determining the electrical resistance of the thermistor TH. The thermistor TH can have a negative temperature coefficient and thus behave like a NTC or have a positive temperature coefficient and thus behave like a PTC.

In an embodiment, the thermistor TH is made of platinum and as a consequence of that has a large temperature range and a linear behaviour. Such a resistive temperature device is sometimes referred to as PTxxx, where xxx indicates the electrical resistance of the platinum thermistor in Ohms at 0 degrees Celsius. Examples are a PT100 and PT500 which respectively have an electrical resistance of 100 Ohms and 500 Ohms at 0 degrees Celsius.

The thermistor TH is connectable to a measuring device (not shown) configured to derive the temperature of the thermistor TH from its electrical resistance. The resistive temperature device RTD therefore comprises two connection leads CL connected to the thermistor TH and extending from the thermistor TH to the proximal end PE. In an embodiment, the connection leads may be connected to a connector at the proximal end PE which allows the resistive temperature device RTD to be connected to a measuring device via an appropriate other cable. In this embodiment, the connection leads CL extend through the proximal end PE and may be connected to a measuring device directly or via an external connector.

The above described two connection leads CL allows a two-wire configuration which is advantageously as it allows easy measurements. However, this configuration also measures the electrical resistance of the connection leads CL. In a preferred embodiment, the resistive temperature device RTD has a three-wire configuration or a four-wire configuration with respectively three or four connection leads CL, which allows to estimate, measure or ignore the electrical resistance of the connection leads CL and thus provides for a more accurate measurement of the electrical resistance of the thermistor TH.

In this embodiment, the thermistor TH is embedded in thermal grease TG that is arranged inside the container EC between the thermistor TH and the surrounding walls W of the container EC. The thermal grease TG ensures that a good thermal contact is achieved between the thermistor TH and the container EC so that the temperature of the thermistor TH is a measure for the temperature of the distal end DE of the container EC, thereby being able to accurately and quickly measure the temperature of the distal end DE of the container EC. The thermistor TH may be in direct contact with the wall portion W closing off the container EC at the distal end, but preferably, the thermal grease TG is completely surrounding the thermistor TH to ensure proper thermal contact at each side of the thermistor TH. In other words, the container EC comprises a first compartment FC near the distal end DE over a length L1 which contains the thermistor TH and is filled with thermal grease TG.

The resistive temperature device RTD further comprises a thermally isolating material TIM arranged inside the container EC between the thermal grease TG and the proximal end PE of the container EC to provide a thermal insulation between distal end DE and proximal end PE of the container EC. In other words, the container EC comprises a second compartment SC extending between the proximal end PE and the first compartment FC over a length L2 which is filled with thermally isolating material TIM. In this way, the connection leads CL extend from the from the thermistor TH to the proximal end PE via the first and second compartment FC,SC.

The thermal grease TG has the advantage that it increases the thermal contact between the thermistor TH and the container EC, thereby allowing to more accurately measure the temperature of the distal end DE of the container EC in relation to a resistive temperature device RTD not comprising thermal grease TG between the walls W of the container EC and the thermistor TH.

The thermally isolating material TIM has the advantage that the thermal resistance between distal end DE and proximal end PE of the resistive temperature device RTD is increased thereby allowing the distal end DE and thus the thermistor TH to more quickly match the temperature of the surroundings. This is the result of the reduced heat capacity of the distal end DE of the resistive temperature device RTD which now requires less heat for a given temperature rise. Further, it keeps the heat at the distal end of the resistive temperature device so that the temperature of the distal end DE more closely matches with the temperature of the surroundings and no additional hot spots are created which could be an ignition source for a dust explosion. In prior art resistive temperature devices too much heat leaks away via the resistive temperature device to accurately measure the temperature.

In order to further increase the thermal resistance between distal end and proximal end, the walls of the container EC are preferably thin compared to the diameter D of the container EC. The thin wall will allow easy heat transfer in the radial direction at the distal end to the thermistor, but will not easily allow heat transfer in the longitudinal direction. As a result, it is possible to use a container made mostly of heat-conducting material, e.g. brass.

In an embodiment, the thermally isolating material TIM is also electrically isolating to electrically isolate the connection leads CL from each other and from the walls of the container EC.

In an embodiment, the thermally isolating material is an inorganic mineral powder.

The second compartment SC may be divided into two subcompartments where one subcompartment is filled with one thermally isolating material and the other subcompartment is filled with another thermally isolating material. For example, a first subcompartment may be provided adjacent the first compartment that is filled with inorganic mineral powder, and a second subcompartment may be provided between the first subcompartment and the proximal end PE that is filled with a thermally isolating resin.

Fig. 2 depicts a partial schematic cross-sectional view of a resistive temperature device RTD according to another embodiment of the invention. Fig. 2 only shows a distal end DE of an elongated container EC and a portion of the resistive temperature device RTD attached to said distal end DE. The distal end DE of the container EC comprises a wear portion WP which has a length L3 that is significantly larger than the wall thickness of the container EC. Next to the wear portion WP, the container EC comprises a first compartment FC over a length L1 with a thermistor TH. The first compartment FC is filled with a thermal grease TG.

The wear portion and the wall portions of the container at the first compartment may be integrated into one piece and thus be made of a single heat conductive material, e.g. brass. Next to the first compartment FC is a second compartment SC similar to the embodiment of Fig. 1 that is filled with a thermally isolating material TIM1 ,TIM2 is provided. The wall portions of the container at the second compartment may have a different thickness and may be made of a different material. Preferably, the wall portions of the container at the second compartment are thinner than the wall portions at the first compartment. Preferably, the material of the wall portions of the container at the second compartment is stainless-steel.

The second compartment is divided into a first subcompartment SCa which is filled with a thermally isolating material of a first kind TIM1 , e.g. quartz sand, and a second

subcompartment SCb which is filled with a thermally isolating material of a second kind TIM2, e.g. an inorganic mineral powder.

The advantage of the wear portion WP is that the distal end DE of the resistive temperature device RTD may wear for a length L3 without damaging the thermistor TH. This allows to use the resistive temperature device RTD in a harsh environment in which for instance a lot of frictional contact is present without requiring to replace the resistive temperature device RTD too quickly.

In the embodiment of Fig. 2, a four-wire configuration is shown in which four connection leads CL are provided to connect the thermistor TH to a measuring device. Two connection leads CL are then connected to one side of the thermistor TH and the other two connection leads CL are connected to the other side.

In an example, the length L3 is 3mm, L1 +L3 is 8mm, the length of the first subcompartment SCa is 12mm and the length of the second subcompartment SCb is 40mm.

The resistive temperature device RTD according to the invention, of which examples are shown in Figs. 1 and 2, can advantageously be used in misalignment sensors according to the invention, examples of which will be shown with reference to Figs. 3A, 3B, 4 and 5.

Fig. 3A depicts a front view of a misalignment sensor BMS according to an embodiment of the invention. The misalignment sensor is based on the principle that when belt

misalignment occurs this results in frictional contact between conveyor belt and

misalignment sensor thereby heating the misalignment sensor which heating can be measured using the resistive temperature device according to the invention. Fig. 3B depicts a cross-sectional view of the misalignment sensor BMS of Fig. 3A along line A-A'. The description below will refer to both Figs. 3A and 3B.

The misalignment sensor BMS comprises a mounting part MP with which the misalignment sensor BMS can be mounted to a stationary part of a conveyor system, where stationary means that the conveyor belt for which the misalignment is measured is moveable relative to the stationary part. The mounting part MP has mounting holes MH, in this case four mounting holes MH to mount the misalignment sensor to the stationary part. The misalignment sensor BMS further comprises a friction part FP with an engagement surface ES for frictional contact with the conveyor belt during misalignment of the conveyor belt. Thermal isolation Tl is provided between the friction part FP and the mounting part MP to thermally isolate the friction part FP from the mounting part MP. Extending through the mounting part MP, thermal isolation Tl and the friction part FP is a bore BO in which a resistive temperature device can be received according to the invention until the distal end thereof lies flush with the engagement surface ES. A container of the resistive temperature device may comprise a stop collar to automatically align the distal end with the engagement surface when introducing the resistive temperature device in the bore BO. The resistive temperature device is configured to measure the temperature of the friction part as a result of the frictional contact between engagement surface of the friction part and the conveyor belt.

Extending through the mounting part MP, thermal isolation Tl and the friction part FP are also two mounting holes MH2 which are able to receive a bolt of a bolt-nut combination to allow the clamping together of the sandwich of mounting part MP, thermal isolation Tl and the friction part FP by the bolt-nut combination. Other attachment configurations are also envisaged. The friction part FP is preferably made of brass. Further, the length L1 +L3 of Fig. 2 or the length L1 of Fig. 1 may match with the thickness of the friction part.

Fig. 4 depicts a cross-sectional view of a misalignment sensor BMS according to another embodiment of the invention. Shown are a friction part FP, a mounting part MP and a thermal isolation layer Tl in between the friction part and the mounting part. The friction part comprises an engagement surface ES for frictional contact with a conveyor belt during misalignment. The friction part further comprises two holes through which screws SR can be inserted to cooperate with threaded holes H01 in the thermal isolation thereby attaching the friction part to the thermal isolation.

The mounting part comprises two holes through which two screws SW can be inserted to mate with threaded holes H02 in the thermal isolation thereby attaching the thermal isolation to the mounting part. As the threaded holes H01 associated with the friction part and the threaded holes H02 associated with the mounting part are provided separate from each other, no heat can leak away via the connection elements SR and SW as they are also separated from each other by the thermal isolation.

The mounting part further comprises mounting holes MH that can be used to mount the misalignment sensor to a stationary part of a conveyor system.

Extending through the mounting part, thermal isolation and friction part is a bore BO to receive a resistive temperature device according to the invention. The bore portion BOM at the mounting part is a little larger and threaded so that an adapter can be fitted into the bore that allows to press fit the temperature device into the bore.

Figure 5 depicts a front view of a belt misalignment BMS according to yet another embodiment of the invention. The view of Fig. 5 is similar to the view used in Fig. 3A. The misalignment sensor of Fig. 5 is of the cylindrical type and thus comprises a circular or cylindrically shaped friction part FP with engagement surface ES.

The friction part is attached to a mounting part MP via a thermal isolation that can not be seen in this figure but which is provided similar to Fig. 3B and Fig. 4.

The friction part is attached to the thermal isolation via screws SR. A resistive temperature device according to the invention can be received in a bore BO to measure the temperature of the friction part. The misalignment sensor can be attached to a stationary part of a conveyor system using mounting holes MH.

A misalignment sensor BMS according to the invention can be used in a conveyor system of which a part is shown schematically in Fig. 6. The conveyor system comprises an endless conveyor belt CB and a conveyor belt carrying element CE. A similar conveyor belt carrying element CE may be provided at the other end of the endless conveyor belt CB. In this embodiment, the conveyor belt carrying element CE is a rotatable drum which is supported via bearings BE.

The conveyor system can be used for many applications, but in this example it is suitable for bulk handling, especially in situations of dust explosion risk environments. The conveyor system further comprises stationary parts SP which in this case extend along each side of the conveyor belt CB. Mounted to each stationary part SP near the conveyor belt carrying element CE is a misalignment sensor BMS according to the invention.

When the conveyor belt is centered with respect to the rotatable drum CE, there is no frictional contact between the conveyor belt and any of the misalignment sensors BMS. However, misalignment of the conveyor belt can occur in two directions as indicated by arrow A1 . When the conveyor belt moves to the right of Fig. 6, it will start to touch the engagement surface of the misalignment sensor. Due to movement of the conveyor belt with respect to the stationary part and thus the misalignment sensor, there will be frictional contact resulting in heat generation and thus a raise in temperature of the engagement surface. In reaction to that measures may be taken to counteract the misalignment, for instance by pivoting the rotatable drum about a longitudinal direction of the conveyor belt portions in between the conveyor belt carrying elements. If this does not help or does not help in time, the temperature may rise to a first danger level which can be used to stop the supply of bulk material to the conveyor as a first measure to prevent a dust explosion. If the temperature rises to a second danger level which is higher than the first danger level, for instance to above 80 degrees Celsius, it may be necessary to stop the conveyor system, i.e. stop movement of the conveyor belt in order to take a further measure to avoid a dust explosion.

It is also possible that the bearings of the rotatable drum fail and that a sudden sideways movement of the drum occurs resulting in a lot of damage. This sudden movement of the rotatable drum can also be detected by the misalignment sensor if the misalignment sensor is arranged such that the sideways movement or the sideways movement in combination with the rotation of the drum results in the separation of the friction part including the portion of the resistive temperature device supporting the thermistor so that suddenly an infinite electrical resistance is measured due to the absence of the thermistor which indicates that there is something wrong and can be used to immediately stop the conveyor system. A similar configuration of misalignment sensors can be provided at the other (not shown) conveyor belt carrying element, so that sideways movement of the conveyor belt can be properly measured at both conveyor belt carrying elements. Although not explicitly shown, the bore BO in which the temperature devices can be received can be a blind bore which ends at or in the friction part.