Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
1998-06-22
2001-02-20
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C324S725000
Reexamination Certificate
active
06190039
ABSTRACT:
TECHNICAL FIELD
The invention relates to a heated type sensor such as an oxygen or a NOx gas sensor.
BACKGROUND OF THE INVENTION
In a heated type sensor in which a sensing portion of an oxygen or a NOx sensor is heated by a heater, the characteristics of the sensing portion are dependent on its temperature which will vary due to the variation of temperature of the environment or the heater's own temperature variation. A conventional temperature control method for heater in which the heater temperature is maintained to a predetermined value, for example, 300-400° C. is described in the JP-A-60 114,758 official gazette.
The heated type sensor maintains constant temperature of a detective part (
3
) with a main heater (
30
) and an auxiliary heater (
32
). A leakage current originating in the deterioration of the insulation substrate (
2
) is absorbed by a guard heater.
The good thermal conductivity (high thermal conductivity) insulation substrate or film (
2
) contains the detective part that is maintained at the high temperature, for example, 400° C., and main and auxiliary heaters are nearly arranged. Alternatively, a guard heater for the leakage current protection is arranged between the main and auxiliary heaters adjacent to the auxiliary heater. A bridge circuit (
18
) contains the auxiliary heater in one side, and first, second and third resistors (
12
,
14
,
16
) in the remaining three sides. The pyro-control circuit comprises an amplifier or a voltage follower (
20
) which supplies a voltage to the main heater, and another amplifier (
24
) having an inverting input connected to a serial node between the first resistor and the auxiliary heater, a non-inverting input connected to another serial node between the second and third resistors, and an output end connected to a control input end of the voltage follower. This amplifier controls the power supply voltage to the bridge circuit and the main heater based on the output of the bridge circuit. The second amplifier (
52
) controls the voltage of a node (
50
) with the guard heater to be identical to that of the node (
13
) with the auxiliary heater, based on an output of the second bridge circuit (
44
) containing auxiliary heater and guard heater (
40
). (See FIG.
4
).
In the aforementioned temperature control method, a thermometric element is disposed adjacent to the heated type sensor with a space therebetween containing gas or ambient air to measure its environmental temperature, and the temperature of the sensing portion is constantly maintained by controlling a power supply to the heater based on the measurement value. The method necessitates the thermometric element by which the temperature of ambient air should be measured, and complex heated type sensor structure and heat control circuitry resulting in higher cost.
Further, an indirect thermal measurement of the sensing portion cannot result in high accuracy because under the condition of gas or air flow through the space, the temperature of the sensing portion is not precisely transferred to the element, and also a delay of temperature transfer to the element can possibly lead to uncontrollable situation such as temperature convergence or divergence.
As another conventional example without any auxiliary heater, a tin oxide film gas sensor is disclosed in 111 page of Nikkei Electronics issued on Jan. 20, 1992 by Nikkei BP publisher. The gas sensor provides four silicon film substrates projected inwardly from a comer of a center-scooped rectangular silicon dioxide substrate chip, and the tin oxide film and platinum heater are deposited on one side of each of the silicon film substrates. The present inventor proposed some improvement regarding the above method in Japanese Patent Application No. 7-328,395.
FIG. 1
shows an example of a well-known bridge type heat control circuit. The circuit comprises a bridge circuit
18
having, for example, a platinum film heater
10
on one side thereof and the resistors
12
,
14
and
16
on the remaining three sides thereof, respectively, an emitter follower
20
which supplies a voltage to the bridge circuit
18
, and an amplifier
24
having its inverting input connected to a serial node
13
between the resistor
12
and the heater
10
, a non-inverting input connected to another serial node
17
between the resistors
14
and
16
, and an output connected to the base of the emitter follower
20
through a resistor
22
.
Resistance value of the platinum film heater
10
is changed with temperature as the temperature T—resistor R characteristics of FIG.
2
. If electric potential values of the serial nodes
13
and
17
are e1 and e2, respectively, the amplifier
24
and the emitter follower connected transistor are so operated that the electric potential e1 is identical to the electric potential e2, i.e., the resistance ratio of the resistor
12
to the heater
10
is identical to that of the resistors
14
to
16
to maintain the temperature of the heater
10
to a predetermined value.
Then, when the temperature of the heater
10
is lower than the predetermined value, output voltage of the amplifier
24
and emitter follower
20
are increased under the condition of e1<e2 to filter increase the power supply to the heater
10
. When the temperature of the heater
10
is higher than the predetermined value, output voltage of the amplifier
24
and emitter follower
20
are decreased under the condition of e1>e2 to decrease the power supply to the heater
10
.
As described above, it is obvious that the bridge type heat control circuit shown in
FIG. 1
has following problems. In order to detect temperature change, i.e., resistance change of the heater
10
precisely, the resistor
12
having higher resistance value than that of the heater
10
may be used. In that case, however, the heat quantity generated in the resistor
12
is also increased more than that in the heater
10
. Thus the energy loss by the resistor
12
is increased, the temperature increase of the resistor
12
simultaneously becomes excessive, and then dangerous.
Since the resistance value of the reference resister
12
changes according to its temperature coefficient, it is difficult to obtain an appropriate heater temperature. Moreover, in case that the resister
12
has a positive temperature coefficient of resistance, the temperature and thus the resistance value of the resister
12
are increased when the heater
10
is heated. Therefore, the settling time to e1=e2 is delayed.
BRIEF SUMMARY OF THE INVENTION
Therefore, it is a first object of the present invention to provide a high reliable and low power consumption heated type sensor which is enabled to maintain a predetermined heater temperature by using main and auxiliary heaters even if an environment temperature is changed.
A second object of the present invention is to provide high reliable heaters and those heat control circuits for the heated type sensor in which an leakage current of the main heater does not influence an auxiliary heater even if the electric insulation of the substrate is deteriorated, and thus the main heater can hold a predetermined temperature.
According to the invention, the heated type sensor comprises main and auxiliary heaters arranged adjacent to the sensing portion to heat the sensing portion to a predetermined temperature. These resistance values of the heaters are so determined that a current to the main heater is, for example 10 times, more than that of the auxiliary heater.
In one preferred form of the present invention, the heated type sensor further includes a guard heater arranged on the insulating substrate adjacent to the auxiliary heater between the main and auxiliary heaters. Though the resistance values of the auxiliary and guard heaters are determined higher than that of the main heater, the heater materials are same as that of the main heater. Therefore, these heaters are formed by different mask patterns in case that a predetermined heating element metal is applied or deposited for the same deposition time. Alternatively, the thick
Gutierrez Diego
Hopgood, Calimafde Kalil & Judlowe
Kabushiki Kaisha Riken
Pruchnic Jr. Stanley J.
LandOfFree
Heated type sensor with auxiliary heater in bridge circuit... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heated type sensor with auxiliary heater in bridge circuit..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heated type sensor with auxiliary heater in bridge circuit... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2585442