DD237898A1 - CIRCUIT ARRANGEMENT FOR INCREASING THE MEASURING VALUE IN TEMPERATURE MEASUREMENT TECHNOLOGY - Google Patents

Abstract

The invention relates to a circuit arrangement for increasing the measured value resolution as a function of the measurement task and the required accuracy in particular for applications in temperature measurement, whereby a significant improvement in the accuracy and Linearitaet the measurement results can be achieved with reduced circuit complexity. This is achieved by switching the resolution of the measuring amplifiers from a central digital measured value processing unit as a function of the absolute height of the temperature measuring signal in such a way that the accuracy of the measurement result in certain, freely selectable ranges is universally adaptable to the process requirements.

Description

Explanation of the essence of the invention:

It is the object to provide a temperature measuring device, which realizes an increase in the resolution and accuracy of the measuring circuit using one and the same temperature sensor even when used in large temperature ranges.

According to the invention this object is achieved in that the circuit arrangement of a temperature transducer, an associated preamplifier and a number of η downstream switchable range amplifiers, an analog / digital converter and a programmable measuring and control device (eg microcomputer) with an associated binary There is an input / output module via which the programmable measuring and control _device can record the temperature measuring signal x _T and output control signals χ _3Ί .... x _Sn to the switchable range _amplifiers .

In this case, the transducer is connected to the input of the associated preamplifier and its output to all inputs of the downstream switchable range amplifier whose outputs are interconnected and in turn connected to the input of the analog / digital converter, the binary converted temperature measurement signal via an input / output Assembly of the programmable measuring and control device supplies.

The programmable measuring and control device is additionally connected via control lines to the switchable range amplifiers and thus switches on the area amplifier responsible for the respective area of the temperature measuring signal. Each range amplifier is preset in gain and offset such that at its output in the associated Meßsignalbereich the same output signal amplitude is generated, with which the subsequent analog / digital converter in the entire, its resolution corresponding number range is controlled.

The advantage of the inventive solution is that by incorporating a programmable control unit in the operations of the measured value and the modularity of the circuit maximum flexibility and adaptability of the measurement of process-related different measurement tasks over a large Temperaturmeßbereich and the respective accuracy requirements when using one and the same temperature sensor is reached. The circuit arrangement according to the invention is suitable for possible application of any sensor and transducer principles in particular for the measurement in large temperature ranges with high-precision resolution of desired portions and thus meets the requirements of a variety of measurement tasks.

embodiment

The invention will be explained in more detail below on a Ausführüngsbeispiel. The accompanying drawings show:

Fig. 1: The basic circuit of the circuit arrangement according to the invention for switchable Meßwertauflösung for η

2, the basic circuit of an embodiment of the inventive circuit arrangement with programmable

2 operational amplifiers, Fig. 3: the range division for the embodiment of Fig. 2 for programmable applications

FIG. 4 shows the profile of the output characteristics of the range amplifiers for the application application according to FIG. 3. FIG.

The basic circuit shown in Fig. 1 consists of a Temperaturmeßwandler 1, a respective transducer type corresponding preamplifier 2, a subsequently arranged group 3 of η switchable range amplifiers BV ₁ ... BV _n , an analog / digital converter 4, a programmable digital Meß and control unit (microcomputer MR) with associated input / output module (EAB) 6.

The operation of the circuit arrangement shown in principle is the following:

The temperature measuring Xj is converted via the transducer 1 into an electrical signal Χι and the input of a transducer type corresponding preamplifier 2 is supplied, which generates a measurement signal proportional to the signal proportional X ₂ , which simultaneously reaches the inputs of all η switchable range amplifier BV ₁ ^ BV _n ,

The switchable range amplifiers are preset in such a way that they generate an output signal X ₃ in the respectively to be resolved measuring signal range, which sweeps over the signal level necessary for full modulation of the downstream analog / digital converter 4. The binary converted measuring signal x ₄ is fed via the input / output module 6 of the programmable measuring and control unit 5, which in turn depending on the applied measuring signal and the existing control program via the control signals x _s1 ... x _Sn one of the switchable range amplifier - And all other switchable range amplifier turns off, so that in the entire temperature range to be detected individual nestable subregions with increased accuracy at full resolution of the analog / digital converter can be set.

The basic circuit shown in Fig. 2 shows an embodiment of the circuit arrangement according to the invention for two measuring ranges in which as switchable range amplifier 3 integrated programmable operational amplifier are used whose output parameters can be influenced via a control input (set-current).

The coupling of the range amplifier to transducer 1, preamplifier 2, analog / digital converter 4 and microcomputer 5 is done in the manner already described.

The range amplifiers BV1 and BV2 can be preset via the resistor circuit (R 11, R12, R13 or R21, R22, R23) in their gain and by the coupling of the voltages Uoi or U ₀₂ in the offset, so that they for each detecting temperature range (input voltage range Ui) provide the full resolution of the analog / digital converter 4 corresponding output voltage range U ₂ .

In the illustrated embodiment, the microcomputer switches via a binary control line x _s using the switching transistors VT1 and VT2 and the inverter N1 via the set inputs of the programmed operational amplifier each one of the range amplifier to. The other range amplifier is then high impedance at its output and does not affect the measurement result.

Fig. 3 shows a possible range division for the embodiment of Fig. 2, which can be used in particular for programmable temperature control devices, which have to regulate the temperature in a wide range, wherein in a limited temperature range increased tasks on the accuracy of the measured value detection ,

Shown is a possible temperature profile over time in the working chamber of an apparatus for cryopreservation of biological material. From the associated temperature measuring a Gesamtbreich T ₀ to T _{3 must be} detected.

Increased demands on the accuracy of the temperature control and thus herherer measurement in the illustrated case in the temperature range between T ₁ and T ₂ . The range amplifiers BV1 and BV2 are thus to be set such that BV1 in the temperature range T ₀ -T ₃ and Bv 2 in the temperature range T ₁ -T ₂ provides a output voltage change corresponding to the modulation of the analog / digital converter (U _2m j _{n -U 2max} ).

Fig. 4 shows the associated dependence of the output voltages of the range amplifiers BV1 and BV 2 on the temperature to be detected for the embodiment of Figs. 2 and 3. The output voltage values U _2m i _n and U _2max represent the modulation _{limits of} the downstream analogue to digital converter.

The output characteristics of the range amplifiers BV1 and BV2 are characterized by relations (1) and (2):

for BVI: U ₂ = V ₁ (U ₀₁ + KT) (1)

for BV2: U ₂ = V ₂ (U ₀₂ + KT) (2)

where V ₁ and V _{2 represent} the gain factors, U ₀₁ and U _{02 represent} the offset voltages of the range amplifiers. The factor K is a combined constant transmission factor of sensor, transducer and preamplifier. In the application shown, the microcomputer can, starting from the measuring signal of the range amplifier BV1 (coarse range) in the temperature range between T ₁ and T ₂ (fine range), activate the range amplifier BV2 and thus gain a measuring signal with increased resolution when the analogue / digital converter is fully utilized.

Claims (1)

Invention claim: Circuit arrangement for increasing the Meßwertauflösung preferably in the Temperaturmeßtechnik when using microcomputers for measured value processing with high demands on the accuracy of the measured value in large temperature ranges, consisting of a Temperaturmeßwandler 1, an associated preamplifier 2, an analog / digital converter 4, a programmable Meß - And control device 5 with associated input / output module 6, characterized in that in addition a number of switchable range amplifiers 3 is present, the transducer 1 is connected to the input of the associated preamplifier 2 and the output to all inputs of the switchable range amplifier 3 whose outputs are connected together and placed at the input of the analog / digital converter 4, which supplies the measuring signal via the input / output module 6 of the programmable measuring and control device 5, which in addition via control lines with the other switchable range amplifiers 3 is connected and controls them such that in each case depending on the measuring range to be detected one of the switchable range amplifier on and all other switchable range amplifiers are turned off, each range amplifier is preset so that at its output in each case to be detected Temperature range one and the same, to Vollaussteuerung the analog / digital converter 4 necessary output signal range is generated. For this 3 pages drawings Field of application of the invention The invention relates to a circuit arrangement for switchable Meßwertauflösung in the process measuring, preferably in the use of microcomputers for measured value processing in temperature measurement. Characteristic of the known technical solutions Electronic temperature measurement techniques have become increasingly important in many areas of research and industrial practice. Questions of measurement accuracy and sensor linearity are increasingly in the focus. Temperature measuring methods of high accuracy and linearity are usually limited from the outset to smaller temperature ranges (eg, BRD-OS 2519335). When it is necessary to detect large areas, compromises with regard to the achievable absolute measuring accuracy are unavoidable. For the realization of electronic temperature measuring devices, a variety of sensor types are known, which differ from one another by the way the temperature is converted into an electrical signal (active, passive) and by the physical operating principles {e.g. B. thermocouple, ohmic resistance, PN junction, etc.). However, all sensor types have more or less pronounced limitations with regard to the linearity and reproducibility of their output characteristics. Therefore, a variety of arrangements are known which compensate for the occurring and accuracy affecting sensor nonlinearities by electronic circuitry. This is z. B. achieved by the fact that in the following after the sensor amplifier circuits by the use of non-linear components a complex compensation of the Meßfühlernichtlinearität takes place (eg SU-PS 1120179, DDR-WP 138820). Other known technical solutions use as a sensor components with the greatest possible linearity without Linearisierungsmaßnahmen, z. As field effect transistors (BRD-OS 2519335), transistor oscillator (BRD-OS 2206089), the accuracy of the measuring method and the resolvable temperature range is limited from the outset. Other known technical solutions, which are characterized by considerable circuit complexity, use for the linearization of the analog circuit programmable read-only memory in conjunction with A / D and D / A converters (eg DDR-WP 215631). To improve the applicability of the temperature measurement, digital measuring methods have tended to prevail (for example, BRD-OS 2905882). Including a programmable digital Meßwertverarbeitungseinheit (microcomputer) software solutions for linearization of the probe characteristic are known (DDR-WP 206176). In other technical implementations, the measured value processing unit intervenes as a control device in the process of measured value acquisition. Methods are known in which, to increase the accuracy over a wide temperature range, different sensors are optionally switched on, which results in increased complexity in the design of the sensor (for example, Federal Republic of Germany Patent Application No. 3,022,942, SU-PS 1101690). Other known solutions influence the time regime of the temperature measurement (sampling rate) as a function of the measurement result, in particular during heating and cooling processes (eg DDR-WP 137755), without the measured value processing unit influencing the accuracy of the resolution of the measured values. Object of the invention The aim of the invention is to avoid the disadvantages of the known technical solutions and to provide a temperature measuring device which exploits their possibilities for increasing the accuracy of certain measuring ranges when using programmable Meßwertverarbeitungseinheiten (microcomputer) and thus to an extension of the scope and applicability of Temperaturmeßschaltungen for large temperature ranges with high accuracy requirements leads.