A DEVICE FOR TEMPERATURE MEASUREMENT AND CONTROL

Abstract: A device for temperature measurement, control and transmission, for use in the industrial field, comprising a sealed container (3) including a logical microprocessor unit (4) and a close-packed and flexible mineral insulation cable (2), all of them forming a monolithic body. The calibration is performed by programming the microprocessor unit, in order to avoid the problems caused by using thermal drift trimmers.

Description: " A DEVICE FOR TEMPERATURE MEASUREMENT AND CONTROL " This invention concerns a device for temperature measur¬ ement and control in industrial plants, in particular where use of programmable logic devices (known as PLC) is anticipated. Many devices are known for measuring a temperature, comprising a probe or a transducer, adapted to provide as an output an electrical signal (usually an analog type signal) corresponding to the measured temperature value. These devices are associated with an amplifying unit and possibly with control and/or coding circuits in order to provide thermostatic transmitting or displaying devices (thermometers) , or to be integrated in a more general control system. A drawback affecting all of these known devices is the fact that the components are available as individual • components, usually manufactured by different companies. This causes a negative influence on the complete system performance. In fact, even though the single pieces have narrow manufacturing tolerances, the tolerance of the complete device comes out to be much larger (as a summation) , and in any case there is lef in addition an unavoidable sensiti¬ vity to drift problems (in time and operation) which cannot be evaluated, and therefore are impossible to be compensated, thus worsing the overall performance thereof. More particularly, in the conventional temperature monitoring systems the following error causes may be detected: 1. drift in time of the active and passive components; 2. undesired thermoelectric effects and/or an incorrect cold junction compensation; 3. drifts caused by variations in the behaviour of the electronics versus temperature; 4. interchangeability tolerance of the sensing member. It is an object of this invention to overcome the limit¬ ations and the drawbacks of the state of the art, as mentioned above, and in particular to provide a mono¬ lithic device, highly precise and stable in time, and having a low cost for a more widespread utilization. Since any mechanical adjustment is missing (potent¬ iometers, trimmers, and so on) , also the device relia¬ bility is consequently improved. This invention meets these objects by means of a device for temperature measurement and control including a temperature probe r a unit for processing the signal provided by said probe, and an electrical connection cable, characterized in that it comprises a sealed container incorporating a microprocessor logic unit and a close-packed and flexible cable provided with mineral insulation, forming a monolithic assembly. According to a first embodiment, the device may be used as a thermostat, i.e. as a device adapted to react by opening or closing a contact once a predetermined precise temperature has been reached. According to a second embodiment, the device provides ' a transmitter for a proportional electrical signal which changes linearly versus temperature. According to a third embodiment, the device comprises a temperature measuring device provided with a digital display. This invention reduces the extent of the problems caused by the drift in time of the active and passive compon¬ ents by eliminating the use of trimmers which are the components more often responsible for these problems. T e other causes of error listed above for the known devices, and which are related to the temperature variations both in the sensing and in the electronic portion, are substantially eliminated by the inventive device. This is done through suitable calibration, i.e. by bringing to known and definite temperatures both the sensitive and electronic portions (the latter too containing a temperature sensor) , and by recording in the permanent memory both the internally read data and the reference temperature data. In such a way, there is provided in the device memory a sort of "individual identification card" adapted to characterize the overall 'behaviour of the sensor and providing the sure basis for all possibile interpolations. The above features and additional ones will become more apparent, together with the related advantages, from the following description of preferred but non limiting embodiments of the inventive device, taken together with the attached drawings, wherein: Figure 1 is a partially sectional side view of the devi- ce according to the invention; Figures 2 and 3 are a side and top plan views, respectiv¬ ely, of a further embodiment of the inventive device. Figure 1 shows the inventive device with a construction suitable to be used both as a thermostat and as a temperature data transmitter. The device shown therein includes a temperature probe, or sensitive member 1, received at the end of a segment of cable 2 having a close-packed mineral insulation, and whose opposite end is integrally fastened to a sealed container 3 housing a processing and control unit 4, in particular a logic microprocessor based unit. The opposite end of container 3 carries a standard type sealed connector 6 adapted to be connected with two or more leads, for the microprocessor unit power supply and the outputs of one or more electrical signals. The temperature probe ia a thermocouple or, as an • alternative, a platinum resistance thermometer. The mineral insulation cable 2 provided with a stainless steel sheath has such a diameter and length to make it stiff enough to bear the assembly, still being flexible, or more precisely deformable in a semi-permanent way, so that the positioning and assembly of the device are made extremely easy. An exemplary length of the cable segment may vary between 100 mm and 1 meter, and even longer for more particular applications. The diameters range between a minimum of 2 mm and a maximum of 8-10 mm. Container 3 comprises a stainless steel cylindrical body integral with cable sheath 5, i.e. permanently ..connected and free from connecting members . Processing unit 4 includes an amplification and analog to digital conversion circuit, and a microprocessor unit including a non-volatile internal-external storage for programming. Connector 6 is liquid-tight and carries 2, 3 or 4 terminals, according to the type of application. Since the device is of a one piece construction, it is easy to take into account the tolerances and the thermal drifts of the components, in order to compensate them through the microprocessor. The drift and offset compensation is obtained by calibrating both the sensitive and logical parts at predetermined reference temperatures, • and by subsequently recording the detected values in the memory. In other words, the device retains in its memory its own single (or intrinsic) characteristic by recording the values detected at the calibration points. In operation, the device will read the detected quant¬ ity, by means of the microprocessor, and it will perform an interpolation relative to the calibration points recorded in the memory. In this way the use of mechanical adjusting means such as trimmers or potentiometers, which may be a cause of instability-and non controllable drifts, is avoided. The calibration of the device is per¬ formed (in a known way ) b means of a suitable programming of the microprocessor unit, in order to recover the errors of both the sensing and electronic portions. According to an alternative embodiment shown in Figures 2 and 3, wherein the same reference numbers have been used to show identical or similar parts to the ones of Figure 1, container 3A has a flat shape, with a diameter larger than the height thereof, and carries a top mounted digital display shown at 9, which makes it possible to read the measured temperature. In this case, the microprocessor unit is arranged (i.e. programmed) for decoding the temperature data and for driving the display . The device does not require any external power supply, in that it is provided with an internal battery 7 and/or with photovoltaic cells sufficient for ensuring the power supply for the entire useful life of the device, therefore it can be installed without any leads and position constraints imposed by the presence of a power supply line. This embodiment too provides the above mentioned features of thermal drift and offset compensation. While this invention has been described herein referring to particular and preferred embodiments thereof, it should not be taken as limited to what has been describ¬ ed herein above, but it is extended to include further variations and modifications which will be apparent to those skilled in this art. o o o c o o o o o o o o o o o o o o o o o o o o o o o o

Claims: CLAIMS • 1. A device for temperature measurement and control, including a temperature probe, a unit for processing the signal provided by said probe, and an electrical connecting cable, characterized in that it comprises a sealed container (3) comprising a logical microprocessor unit (4) and a close-packed and flexible mineral insulation cable (2) r forming a monolithic body. 2. The device of claim 1, characterized in that said temperature probe includes a thermocouple. 3. The device of claim 1, characterized in that said temperature probe includes a platinum resistance thermometer. 4. The device of claim 2 or 3, characterized in that said container (3) ends at one end thereof with a sealed connector (6) . 5. The device of claim 4, characterized in that said container (3) is a stainless steel cylindrical body integral with the sheath (5) of the cable housing the temperature probe. 6. The device of claim 5, characterized in that said microprocessor unit (4) is adjusted to operate as a thermostatic device. 7. The device of claim 5, characterized in that said microprocessor unit (4) is arranged for operating as a device for transmitting an electrical signal represent¬ ing the temperature. 8. The device of claims 2 or 3, characterized in that said container (3A) has a diameter larger than its height and is provided with a digital display (9) or the measured temperature. 9. The device of claim 8, characterized in that said container (3A) is water tight and provided with a power supply battery.

Inventors: NOLI CANZIO, NOLI, CANZIO
Applicants: TESTEL SPA, TESTEL S.P.A.
Application year: 1992
Main classification: G01K1
IPC codes: G01K1, G01K15, G05D23