DE3135853A1 - ARRANGEMENT AND METHOD FOR ELECTRONIC TEMPERATURE MEASUREMENT - Google Patents

Description

PATENTANWÄLTE ZENZ & HELBER ■ D 4300 ESSSN <· AM tR \ j! R £ RSTEifcJ 1 I TEL .. (O2OU 4156 page "" _ ΐ'Γ " * * · _ D 975

DIATEK, INC. . 3910 Sorrento Valley Blvd., San Diego, California, .V.St.A.

Arrangement and method for electronic temperature measurement.

The invention relates to an arrangement and a method for electronic temperature measurement and in particular on an electronic thermometer that gives an accurate reading of quasi-static temperatures to one before stabilizing of the sensor is at the temperature to be measured Time allows. -

Precise and rapid temperature measurements were made by thermal engineers aspired for centuries. The most common type of temperature measuring device consists of one Sensor element, the characteristic of which is a function of the sensor temperature, and a display device that works depending on the temperature characteristics of the sensor. To the temperature "an object under Using such a thermometer to measure, it is necessary to have a temperature flow from the object to the probe takes place until the sensor reaches the temperature of the object. At this point the display shows the temperature of the object according to the accuracy of the measuring system.

Since it takes some time for the heat to pass from one Object to a sensor has taken place is the speed, with which such a temperature is measured

Z / ko.

can be limited by the thermodynamic characteristics of the system. The time required for heat transfer is called the "thermal delay". Often the case axxf occurs that the temperature stabilization of the sensor takes longer than desired, so that in such cases an "exact measurement is sought before the stabilization.

The laws of heat transfer allow such a measurement before temperature stabilization. This was recognized well before the beginning of the 20th century "and there were presented many thermometers for measuring both static and dynamic temperatures for years to come, which the known heat transfer characteristics · of a particular thermal system to achieve Use more precise measurements even though the sensor temperature has not yet reached the measured object temperature. The principle on which these thermometers and their ability to measure temperature more quickly are based is known as Newton's law of cooling. In use on a temperature measurement system, this process is called thermal lag compensation. Sir Isaac Newton discovered 1701 that the rate of temperature change of an object (e.g. a probe) that is in contact with. one is in contact with another object is directly proportional to the temperature difference between the objects. Under Observing this law, it is possible to use a correction factor from the rate of temperature change of the Sensor., Which when added to the current Temperature value of the sensor enables the actual temperature value to be measured by the sensor to be determined, 'even' if the sensor temperature has not yet stabilized is. . "--.- ■" - ■

An early definitive work, .which the. Above principle discussed, was published in the Bulletin of the Bureau of Standards Volume 8, 1913, page 659. This principle has been

»···· ·· ·». «" «Γ« O I O J O U J

then in many devices used in various US patents and other publications sine. In dor US-PS 3,111,03 ?. (Wormser) and the For example, US Pat. No. 3,702,076 (Georgi) describes methods of compensating for thermal delay. A particularly useful device was described by Botshov in ". SU Patent 174,398.

While at first glance it may seem as if the principle of Newton's law of cooling is almost a would allow immediate measurement of the temperature, the aim can be an immediate reading or recording of measured values cannot be achieved in practice for a number of reasons. Depending on the desired measurement accuracy, a Improvement of the reading time by an actuator of 4 'should be considered good.

With each of the known methods mentioned above with Funds-shares a different type of condensation of the applied thermal delay and took a different route to determine when the thermometer reading represents the temperature to be measured. None of these. known methods, however, allows the implementation of the Measurement in the. shortest possible time.

In US ^{Pat. Nos. 1} η 3,111,032 and 3,702,076, the termination of the measuring phase, ie the evaluation of the thermometer display value as the temperature to be measured, is set at a fixed point in time after the start of the measurement. In US Pat. No. 3,702,076, a second exemplary embodiment is described in which the measurement is terminated if the sensor temperature change rate falls below a predetermined value. According to the above-mentioned Russian patent, the measurement cycle is terminated when the rate of change of the sensor temperature times a fixed factor is numerically equal to the actual sensor temperature value.

In all known designs and methods, the point in time at which the measurement is ended has no fixed relationship to the accuracy of the correction factor or to the accuracy of the measurement. Therefore, the time of the end of the measuring cycle must be set conservatively so that the accuracy of the measurement is acceptable under all expected operating conditions. ^; .

The invention is therefore based on the object of ending the measuring cycle in electronic temperature measurement to relate to the measurement accuracy 'and therefore the measurements in the shortest possible time for a given thermal system and given operational parameters perform. In the following the invention will be described with reference to clinical thermometers, i. H. combined with the measurement of human body temperature, although the invention also applies to other applications of the Temperaturmeßtechnik is suitable. The one used in thermometers to determine human body temperature The sensor is typically designed as a thermistor, which is arranged at the distal end of a probe is. A replaceable sterile sleeve is usually used to prevent cross-infection. One electronic circuit with an analog / digital converter and a digital display enables the display of the Sensor temperature plus a correction.

When the probe / sheath combination is placed in the mouth, the probe begins to heat up rapidly. Over time, the sensor temperature is brought closer and closer to the mouth temperature, so that the rate of change the sensor temperature according to the Newtonian Cooling law drops. A representative curve of the sensor temperature over time is shown as' curve 10 in Fig. shown. It can be seen that with the lapse of time after the insertion of the probe, the curve 10 changes

- Ό ftm . · «« ".. * *». * -Ϊ. OI 0 YYY

temperature to be measured asymptotically approaches and after a relatively long time the temperature to be measured has come so close that it is used as a temperature to be measured can be designated.

As stated above, a correction factor can be applied to any instantaneous value of the sensor temperature along the curve 10 can be added to obtain the value of the temperature to be measured. This correction factor is the product of a proportionality factor (known as the thermal time constant) and the change in speed the sensor temperature at this point in time. ' Unfortunately, the thermal time constant is the most

■ thermal systems are not exactly known, and in fact it is usually not a constant at all, but a value that varies within certain limits from measurement to measurement and depending on the initial conditions as well as other factors and also changes as a function of time. Accordingly, a reliable reading of the temperature to be measured not obtained in an early phase of the measurement cycle will. Curve 11 in FIG. 1 shows a representation of measured values over time of curve 10 plus one Correction based on an assumed thermal time constant of the system times the change in speed the sensor temperature. It can be seen that a exact temperature reading can only be obtained after a certain time has elapsed after inserting the sample.

As stated above, this problem has been addressed in the past by using either a predetermined Period of time or the decrease in the rate of change

waiting for the sensor temperature to fall below a sufficiently low value to ensure that the Correction of the sensor temperature measured value. sufficiently small

♦ ·

is so that an inaccuracy of the correction is negligible will. However, none of these methods resulted in a temperature reading in the shortest possible time.

This succeeds only after the teaching of the present invention in that the corrected sensor temperature is monitored and the · measuring cycle is ended when the corrected temperature display reaches a substantially stable value, d. H. if the ad is no more than a predetermined one Value changes during a specified time interval.

As stated above, the "thermal time constant ¹¹ of thermal systems - is not exactly constant, but changes" during the measurement cycle. This is especially true for clinical temperature measurement, since the thermal system is complicated due to the coating or sheathing over the probe. It is possible to improve the speed of the measurement by adopting a variable value of the thermal time constant in the "calculation" of the correction factor of the thermal. Delay instead of a fixed value. In fact, it has been found that ... a special shape a corrective ac'torg calibration, which is given below, comes very close to the characteristics, the usual thermistor and the replaceable sterile sheath in a clinical thermometer.

In the following the invention will be explained with reference to the drawing explained in more detail. In the drawing show:

Fig. 1 is a graph of the curve of sensor temperatures over time as well as the same curve including a correction factor; and

Figure 2 is a block diagram of a preferred embodiment de :; electronic thermometer according to the invention.

In Figure 2, in which a block diagram of a using The thermometer formed according to the invention is shown, a probe 21 with an amplifier 22 coupled. When the clinical temperature measurement is the sensor is typically a thermistor located at one end of a probe, and in operation a replaceable sterile wrap is normally used to prevent cross-infection. A typical sheathed thermistor probe for use in clinical temperature measurement is in • U.S. Patent 4,054,057 (Kluge). The thermistor sensor is usually arranged in a bridge circuit, the output voltage of which is a function of the sensor temperature is. Other types of temperature sensors and other connection circuits of known type can be used in conjunction can be used with the invention.

The amplifier 22 amplifies the output signal of the sensor circuit and supplies a voltage for control of the analog / digital converter (A / D converter) 23. In the embodiment described, the Output of the A / D converter 23 in parallel binary form. A microprocessor 24 takes the output signal of the A / D converter 23 and performs certain mathematical operations on the basis of the supplied data, such as will be described below ..

The digital information representing the sensor temperature, which appears at the output of the A / D converter 23, becomes twice sampled per second by microprocessor 24 and stored in memory

cached. The memory 25 has sufficient storage capacity to store the data representing three consecutive scans. For the arithmetic operations of the microprocessor, data are therefore available which represent three successive temperature measurements. These can be entered with T ₀ , T. and T "

__ of »

^ J I J J υ O J

are designated. The last temperature measurement is Τ «and, the most recent one (2 seconds older) temperature measurement is T_.

If the feeler is in combination with the object whose Temperature is to be measured is a system known as a single time constant system (i.e. if the time constant is actually a constant), so can use the correction factor C every half second can be calculated using the following equation:

• C = A (T _Q - T ₂ )

In this formula the factor (T,. ~ " ^T o ^ * ^n, very precise approximation, is numerically equal to the rate of change of the sensor temperature at time T ,, and A" is the thermal time constant of the system ..

It has been found that one in practical use Clinical thermometer located with a probe and a cover or a wrapper in the US-PS 4,054,057, the thermal system is much more complicated than that in the previous paragraph is the single time constant system described and a more precise value for the correction factor "when used can be obtained from the following equation:

C = B log Cl + A (T ₀ -T ₂ )]

Where A and B are constants whose values differ from the particular ones Characteristics of the respective sensor and the used cover are dependent. For example, are the constants A and B, which have a correction factor C in A close approximation to practicable cover-sensor combinations results in the following values: A = 40 and B = 0.8.

ΛΑ

After determining the correction factor C with the aid of the microprocessor, either one of the above mentioned formulas or a special sensor / thermal system Adapted formula can be used, the temperature to be measured τ (from the microprocessor 24) is below Calculated using the following equation:

^T m ^{= T} l ^{+ C}

T is calculated by the microprocessor every half second and brought to the display 26 for display. Like on the Curve 11 can be seen, T typically grows initially quickly and in some cases even exceeds the actual value of the temperature to be measured. When the sensor temperature however, approaches the temperature to be measured and the correction factor C becomes relatively small, T eventually converges to the actual temperature to be measured.

The calculated values of T will be with the half

m.

The value of T calculated second previously, which is in memory

25 has been saved. These comparisons are performed by the microprocessor 24 every half seconds until the differences between six sequentially comparing each ■ smaller than a vorgeqebener value, for example 0.05 ⁰ F. Six successive differences of less than 0.05 F mean that the value T converges on the temperature to be measured, and at this point in time the temperature measuring cycle is ended, the display is locked and a horn 27 is activated, which signals the user Acknowledges that the value of T then displayed is an exact measure of the temperature to be measured.

The calculation and control functions described above are operations in microprocessor technology that are known per se and are therefore not described in more detail. Of the

Is an expert in the field of microprocessor technology. able to mechanize the functions described in a suitable manner without further information.

An arrangement and a method for Electronic temperature measurement in which the temperature to be measured is calculated during a measurement cycle performed repeatedly and the calculated values compared to determine whether results in a sequence of matching values. A sequence of corresponding calculated temperature values is a sign of an exact temperature display, and if this sequence is established, the measuring cycle is interrupted and the last one calculated Value assumed as a measure of the temperature to be measured.

Claims (5)

PATENTANWÄLTE ΖΕΝ2 & HELBER D 4300 ESSgNJi * IkMiRWiIRSITEIJ ¹ J 1 ° TEL .: (02 01) 41 2G Page - 1 - D 976 DIATEK, INC. Claims l _o , arrangement for electronic temperature measurement with a device for correcting the electrical output signal of a temperature sensor during a measuring cycle as a function of the rate of temperature change of the sensor, the temperature to be measured being represented by the corrected electrical signal, characterized by a) a device for monitoring changes in the corrected electrical signal and b) a device for ending the measuring cycle, controlled as a function of these changes. 2. Method for electronic temperature measurement in which an electrical output signal is provided during a measuring cycle a temperature sensor as a function of the rate of temperature change corrected and the temperature to be measured is represented by the corrected electrical signal is thereby identified that the changes in the corrected electrical signal are monitored and that the measurement cycle as a function will be terminated by these changes. 3. The method according to claim 2, characterized in that the measuring cycle is ended when the corrected electrical signal changes by no more than a predetermined value during a predetermined time interval. Z / k ο. 4- The method according to claim 2 · or 3, characterized in that the corrected electrical signal periodically sampled and the measuring cycle is ended when the values are a predetermined number successive scans do not change more than a specified value. 5. The method according to any one of claims 2 to 4-, characterized marked that the correction of the electrical The output signal of the temperature sensor is essentially based on the following function: A log (1 + BT '), where A and B are constants. and T ^? is the rate of change of the sensor temperature.