- Email: [email protected]
Contactless temperature switch using amorphous ribbons
Journal of Magnetism and Magnetic Materials 102 (1991) 135-138 North-Holland
Contactless
temperature
switch using amorphous ribbons
G. V&-tesy, A. Lovas, J. Sziilliisy and T. Tarn6czi Central Research Institute for Physics, P.O.B. 49, H-1525 Budapest, Hungary
Received 15 April 1991; in revised form 7 June 1991
A device has been developed for a temperature switch. It has two electronic output levels. By characteristically changing the temperature to a certain value, the device goes through a rapid transition from high to low output level. It does not contain moving parts: detection of the required temperature is realized fully electronically. It is based on metallic glasses, of which the Curie temperature can be easily and substantially modified. The switching temperature can be chosen in a wide range, from - 40 to + 150 o C. The thermal hysteresis of the device does not exceed 3 o C.
1. Introduction Temperature switches are widely used for detecting the temperature of the vicinity for a certain part of machinery reaching a critical value. The majority of the commonly used devices use some moving parts, which close or open an electrical circuit. The most conventional type of temperature switch is the bimetal device, where two metals with different thermal expansion coefficient are compressed, and by changing the temperature it is bent. Due to this bending an electric current is switched on or off. When a lower value of thermal hysteresis is necessary, in applications of higher precision, an improved variant is used, or the switch itself is heated by the electric current. Another group of temperature switches is based on the thermal expansion of a gas or liquid in a capillary tube. Also in this case, electric current is switched on or off. Recently, different types of electronic temperature switches have been widely used. Here the sensing elements can be a thermistor or a silicon chip or other materials, of which some electric parameter (e.g. resistance, voltage, current etc.) is modified by changing the temperature. The obtained signal is processed by an electronic unit. In this paper a new, contactless device is described which has been developed only recently. 0304-8853/91/$03.50
It is simple in construction, and it makes possible a fast switching in a wide temperature range with low thermal hysteresis. The production of the device is not complicated, and it is reliable with long endurance. The device has two stable electronic output levels, a high and a low one. By heating (or cooling if the switching temperature is low) the device to a certain temperature, which characterizes the device, a rapid transition takes place from the high to the low output level. The device does not contain moving parts: detection of the wanted temperature is realized fully electronically. The device is based on metallic glasses, of which the Curie temperature can be easily and substantially modified by choosing the appropriate chemical composition. The transition through the Curie temperature is detected.
2. Properties of metallic glass ribbons In the temperature switch, as-quenched amorphous metallic glass ribbons are applied as the basic material. Their advantageous properties, namely the possibility of controllable choice of the Curie temperature, the high initial permeability, the resistance to corrosion and other environ-
0 1991 - Elsevier Science Publishers B.V. All rights reserved
136
G. Wrtesy et al. / Contactless temperature switch
+ WC1
for the materials. At the same time one must keep the x value within +O.l at%. The composition of materials was determined by atomic absorption spectrophotometry, its accuracy in the 1
‘4, , , , , “4, 2
L,
6
8
10
12
Fe&r,,6iB), Tc,,, ( ’ C> X(%)
_
14
Fig. 1. The dependence of Curie temperature, T,, on the Cr content, x, for two systems of amorphous ribbons.
mental effects, good mechanical properties and the well known processing technology make these materials suitable for this purpose. The chemical composition of the applied ribbons are: Fe,,_,TMX(SiB),, and Fess_,TM,B,,, where TM is a transition metal. As was shown earlier [l-3], a drastic change in the Curie temperature T, can be achieved by the replacement of a ferromagnetic host with another transition metal. The main requirement for the material is a stable and reproducible Curie temperature which can be modified extensively with an accuracy of + 2 ’ C. The adjustment of the Curie temperature is made mainly by modifying the composition of the system. The transition metal should be chosen in such a way that it provides a high enough dT,/dx, but this value should not be so high that one cannot find the possibility to fulfil the requirement for the necessary alloying accuracy. These requirements can be satisfied by chasing Cr as a transition metal in the above described compositions. Fig. 1 shows the dependence of Curie temperature on the Cr content, X. As can be determined from the figure, dT,/dn = 27.5 o C% for Fe,,_,Cr,(SiB), and dT,/dx = 21”C% for the Fes5_XCrXB1S system. dT,/dx is high enough to provide a wide temperature range
F%.8%,B15 425
530
It is also very important to keep the processing condition stable, because the physical properties (among them T,) of transition metal-metalloid based metallic glasses are sensitive to the processing conditions [4,5]. It is expedient to choose the operating temperature in such a way that T, -K Ttryst (where T,,st is the crystallization temperature of the metallic glass), because in this case, there is no danger of crystallization during operation. If T, approaches or passes 100 “C, it is necessary to stabilize the Curie temperature by a suitable annealing method. The best result is produced by applying the annealing temperature near the temperature of operation because the equilibrium Curie temperature of metallic glasses generally depends on the annealing temperature. If the Curie temperature is less than say 200 ‘C WC)
I
-
1
II
Ta -IWC
3o0
1
2
3
4
t
(h)
Fig. 2. The dependence of Curie temperature, T,, on the time of annealing for two different annealing temperatures T,, in the case of Fe,,,,Cr,&iB), ribbon.
G. V&tesy et al. / Contactless temperature switch
sensing element
oscillator -
rectifier -
137
cof-nparatw open collector output transistor
b
Fig. 3. The block diagram of the sensor.
then it can be annealed at higher temperature in order to have a shorter annealing time. This method is suitable especially in the case when the reversible relaxation does not change the equilibrium Curie temperature substantially. Such a type of metallic glass can be produced by adding some Cr to a non-magnetostrictive glass as has been pointed out recently [5,6]. A typical change of the Curie temperature due to isothermal annealing is shown in fig. 2.
3. The operation of the device The sensing element of the device is a miniature, high frequency transformer, of which the core is made of metallic glass. The separate secondary winding yields ohmic isolation. As the temperature reaches the Curie temperature, it transforms from a ferromagnetic to a paramag-
1 15
u IV)
II
lo-
II
netic state and so the coupling between the coils decreases significantly. Due to this, the amplitude of the high frequency signal also decreases. After rectification the signal gets to a comparator, which has a hysteresis, and this controls the open collector output unit. Depending on the application, the output can be sink or source up to max. 60 V voltage and to 200 mA current. Fig. 3 shows the total block diagram of the proposed sensor. The electronic unit is realized by a surface mounted method on ceramic wafer. This ensures high reliability and long lifetime, and it forms one unit with the sensing element. The device is potted by epoxy resin, thereby ensuring its resistance to oil, dirt, water and also to mechanical effects. The supply voltage can be 3 to 30 V. The volume of the device is about 1 cm3, the electronic unit is integrated into this volume. Special attention has been given to ensure the best thermal contact between the environment and the amorphous core. The device - depending on the Curie temperature of the amorphous coil - can operate in the -40 to + 150 o C temperature range. The thermal hysteresis does not exceed 3 ‘C. The output voltage as a function of the temperature, is seen in fig. 4. The thermal hysteresis is 1.5 o C.
,
References 5-
HI L. G&&y,
T(‘C) 4 50 loo 150 Fig. 4. The output voltage of a temperature switch, as a function of temperature (USUpplY = 12 VI.
A. Lovas, L. Kiss, T. Kern&y and E. KisdiKoszo, J. Magn. Magn. Mater. 26 (1982) 109. 121H.J.V. Nielsen, J. Magn. Magn. Mater. 19 (1980) 138. [31A. Lovas, L. Potocky, L. Novak, E. Kisdi-Koszd and K. Zambd-Balla, in: Metallic Glasses: Science and Technology, vol. 2, eds. C. Hargitay et al. (Kultura, Budapest, 1980) p. 87.
138
G. V&tesy et al. / Contact&
[4] A. Lovas, 6. Kisdi-Kosz6, L. Potocky and L. Novik, J. Mater. Sci. 22 (1987) 1535. [S] T. Tarnbczi, A. Lovas and C. Kopasz, Mater. Sci. Eng. 97 (1988) 509.
temperature switch
[6] T. Tarnbczi, G. Konczos and Z. Hegediis, J. de Phys. 49 (1988) C8-1271.
Contactless
temperature
switch using amorphous ribbons
G. V&-tesy, A. Lovas, J. Sziilliisy and T. Tarn6czi Central Research Institute for Physics, P.O.B. 49, H-1525 Budapest, Hungary
Received 15 April 1991; in revised form 7 June 1991
A device has been developed for a temperature switch. It has two electronic output levels. By characteristically changing the temperature to a certain value, the device goes through a rapid transition from high to low output level. It does not contain moving parts: detection of the required temperature is realized fully electronically. It is based on metallic glasses, of which the Curie temperature can be easily and substantially modified. The switching temperature can be chosen in a wide range, from - 40 to + 150 o C. The thermal hysteresis of the device does not exceed 3 o C.
1. Introduction Temperature switches are widely used for detecting the temperature of the vicinity for a certain part of machinery reaching a critical value. The majority of the commonly used devices use some moving parts, which close or open an electrical circuit. The most conventional type of temperature switch is the bimetal device, where two metals with different thermal expansion coefficient are compressed, and by changing the temperature it is bent. Due to this bending an electric current is switched on or off. When a lower value of thermal hysteresis is necessary, in applications of higher precision, an improved variant is used, or the switch itself is heated by the electric current. Another group of temperature switches is based on the thermal expansion of a gas or liquid in a capillary tube. Also in this case, electric current is switched on or off. Recently, different types of electronic temperature switches have been widely used. Here the sensing elements can be a thermistor or a silicon chip or other materials, of which some electric parameter (e.g. resistance, voltage, current etc.) is modified by changing the temperature. The obtained signal is processed by an electronic unit. In this paper a new, contactless device is described which has been developed only recently. 0304-8853/91/$03.50
It is simple in construction, and it makes possible a fast switching in a wide temperature range with low thermal hysteresis. The production of the device is not complicated, and it is reliable with long endurance. The device has two stable electronic output levels, a high and a low one. By heating (or cooling if the switching temperature is low) the device to a certain temperature, which characterizes the device, a rapid transition takes place from the high to the low output level. The device does not contain moving parts: detection of the wanted temperature is realized fully electronically. The device is based on metallic glasses, of which the Curie temperature can be easily and substantially modified by choosing the appropriate chemical composition. The transition through the Curie temperature is detected.
2. Properties of metallic glass ribbons In the temperature switch, as-quenched amorphous metallic glass ribbons are applied as the basic material. Their advantageous properties, namely the possibility of controllable choice of the Curie temperature, the high initial permeability, the resistance to corrosion and other environ-
0 1991 - Elsevier Science Publishers B.V. All rights reserved
136
G. Wrtesy et al. / Contactless temperature switch
+ WC1
for the materials. At the same time one must keep the x value within +O.l at%. The composition of materials was determined by atomic absorption spectrophotometry, its accuracy in the 1
‘4, , , , , “4, 2
L,
6
8
10
12
Fe&r,,6iB), Tc,,, ( ’ C> X(%)
_
14
Fig. 1. The dependence of Curie temperature, T,, on the Cr content, x, for two systems of amorphous ribbons.
mental effects, good mechanical properties and the well known processing technology make these materials suitable for this purpose. The chemical composition of the applied ribbons are: Fe,,_,TMX(SiB),, and Fess_,TM,B,,, where TM is a transition metal. As was shown earlier [l-3], a drastic change in the Curie temperature T, can be achieved by the replacement of a ferromagnetic host with another transition metal. The main requirement for the material is a stable and reproducible Curie temperature which can be modified extensively with an accuracy of + 2 ’ C. The adjustment of the Curie temperature is made mainly by modifying the composition of the system. The transition metal should be chosen in such a way that it provides a high enough dT,/dx, but this value should not be so high that one cannot find the possibility to fulfil the requirement for the necessary alloying accuracy. These requirements can be satisfied by chasing Cr as a transition metal in the above described compositions. Fig. 1 shows the dependence of Curie temperature on the Cr content, X. As can be determined from the figure, dT,/dn = 27.5 o C% for Fe,,_,Cr,(SiB), and dT,/dx = 21”C% for the Fes5_XCrXB1S system. dT,/dx is high enough to provide a wide temperature range
F%.8%,B15 425
530
It is also very important to keep the processing condition stable, because the physical properties (among them T,) of transition metal-metalloid based metallic glasses are sensitive to the processing conditions [4,5]. It is expedient to choose the operating temperature in such a way that T, -K Ttryst (where T,,st is the crystallization temperature of the metallic glass), because in this case, there is no danger of crystallization during operation. If T, approaches or passes 100 “C, it is necessary to stabilize the Curie temperature by a suitable annealing method. The best result is produced by applying the annealing temperature near the temperature of operation because the equilibrium Curie temperature of metallic glasses generally depends on the annealing temperature. If the Curie temperature is less than say 200 ‘C WC)
I
-
1
II
Ta -IWC
3o0
1
2
3
4
t
(h)
Fig. 2. The dependence of Curie temperature, T,, on the time of annealing for two different annealing temperatures T,, in the case of Fe,,,,Cr,&iB), ribbon.
G. V&tesy et al. / Contactless temperature switch
sensing element
oscillator -
rectifier -
137
cof-nparatw open collector output transistor
b
Fig. 3. The block diagram of the sensor.
then it can be annealed at higher temperature in order to have a shorter annealing time. This method is suitable especially in the case when the reversible relaxation does not change the equilibrium Curie temperature substantially. Such a type of metallic glass can be produced by adding some Cr to a non-magnetostrictive glass as has been pointed out recently [5,6]. A typical change of the Curie temperature due to isothermal annealing is shown in fig. 2.
3. The operation of the device The sensing element of the device is a miniature, high frequency transformer, of which the core is made of metallic glass. The separate secondary winding yields ohmic isolation. As the temperature reaches the Curie temperature, it transforms from a ferromagnetic to a paramag-
1 15
u IV)
II
lo-
II
netic state and so the coupling between the coils decreases significantly. Due to this, the amplitude of the high frequency signal also decreases. After rectification the signal gets to a comparator, which has a hysteresis, and this controls the open collector output unit. Depending on the application, the output can be sink or source up to max. 60 V voltage and to 200 mA current. Fig. 3 shows the total block diagram of the proposed sensor. The electronic unit is realized by a surface mounted method on ceramic wafer. This ensures high reliability and long lifetime, and it forms one unit with the sensing element. The device is potted by epoxy resin, thereby ensuring its resistance to oil, dirt, water and also to mechanical effects. The supply voltage can be 3 to 30 V. The volume of the device is about 1 cm3, the electronic unit is integrated into this volume. Special attention has been given to ensure the best thermal contact between the environment and the amorphous core. The device - depending on the Curie temperature of the amorphous coil - can operate in the -40 to + 150 o C temperature range. The thermal hysteresis does not exceed 3 ‘C. The output voltage as a function of the temperature, is seen in fig. 4. The thermal hysteresis is 1.5 o C.
,
References 5-
HI L. G&&y,
T(‘C) 4 50 loo 150 Fig. 4. The output voltage of a temperature switch, as a function of temperature (USUpplY = 12 VI.
A. Lovas, L. Kiss, T. Kern&y and E. KisdiKoszo, J. Magn. Magn. Mater. 26 (1982) 109. 121H.J.V. Nielsen, J. Magn. Magn. Mater. 19 (1980) 138. [31A. Lovas, L. Potocky, L. Novak, E. Kisdi-Koszd and K. Zambd-Balla, in: Metallic Glasses: Science and Technology, vol. 2, eds. C. Hargitay et al. (Kultura, Budapest, 1980) p. 87.
138
G. V&tesy et al. / Contact&
[4] A. Lovas, 6. Kisdi-Kosz6, L. Potocky and L. Novik, J. Mater. Sci. 22 (1987) 1535. [S] T. Tarnbczi, A. Lovas and C. Kopasz, Mater. Sci. Eng. 97 (1988) 509.
temperature switch
[6] T. Tarnbczi, G. Konczos and Z. Hegediis, J. de Phys. 49 (1988) C8-1271.