SU1234730A1 - Multichannel digital thermometer - Google Patents

Description

The invention is suitable for temperature measurements and can be used to create high-precision multi-channel digital thermometers for use with different types of thermoelectric converters.

The aim of the invention is to improve the measurement accuracy by providing automatic calibration of the thermometer at different measuring ranges, as well as ensuring that it is possible to work with thermal converters of various types.

The following is a structural diagram of a multi-channel thermometer; Fig. 2 is an example of a specific embodiment of the thermometer.

The thermometer contains a group of thermoelectric converters 1, a source of reference voltage (IN) 2, a switch (K) 3, a current amplifier (UTTG) 4 with a tunable gain factor, an integrated analog-to-digital converter (ADC) 5, programmable timer (T.) 6, gene €; rarer of reference frequency (GI) 7, memory (memory) 8, microprocessor (NI) 9, display device (I) 10.

Thermoelectric converters I and the source of reference voltage 2 are connected to the cat mutator 3, one of the inputs of which is connected to the common point of the circuit. Input UPT 4 is connected to the output of switch 3, and it is connected to the input of ADC 5. The output of programmable timer 6 is connected to the control of the input of ADC 5, and its inputs to the output of pulse generator 7 and microprocessor 9. The remaining three. the output of the MP is connected to the controls of the inputs of the switch 3, the control device 4 and to the display device 10. The inputs of the MP 9 are connected to the outputs of the ADC 5 and the memory of the device 8.

The thermometer operates as follows: 3QM ..; ; : .- ...,,.

The measured temperature is converted with the help of: thermoelectric converters I, supplied to. Bxojiy switch 3 in the EMF. The thermometer can be programmed to work with various types of thermal converters, differing in the measurement range of the output signal.

Thermometer operation begins with an instrument sensitivity calibration.

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For this purpose, the output signal MP 9, the switch 3 connects to the input-UFL 4 a source of reference voltage 2, the value of which is chosen to be approximately equal to the minimum value from a series of maximum output signals of thermal converters.

The sensitivity calibration of the instrument is carried out for all values of the K – UPT gain factors, switched by the output signal of the MP 9. For the purpose of full use of the ADC scale at different measuring limits, the KPT values are chosen from

converting the output range of the 1st thermal converter to a level corresponding to the range of the input voltages of the ADC.

For each measurement limit,

those. for each value of the UFD, the determined duration of the integration time of the input signal of the ADC is set to (n + ha) periods of the network during the yarn,. Wherein

The conversion ratio of the ADC is

S (n4tn.) Sn (l + -), where S is the conversion coefficient of the ADC with an integration time equal to one period of the mains voltage.

The formation of rectangular pulses with a duty cycle of two desired duration, defining the duration of the integration cycle of the input signal of the ADC, is performed by a programmable timer 6 by dividing the reference frequency from the output of the pulse generator 7 by a predetermined factor loaded into timer 6 by MP 9. /.

The output code of the ADC N. in the measurement cycles of the reference voltages C at each measurement limit is determined by the voltage

N, i (U ,. and, n) - (S.n (l + |). (O

where is the zero displacement, reduced to the UPT input.

The measured values of N. are counted with Ml 9 and ASH 5 and are stored in memory 8, "/,

In the offset measurement cycle, the input of the UFT 4 by means of the switch 3, controlled by the MP 9, is shorted to a common point of the circuit. For all values of the gain factors K UPT and for the duration of the integration time of the ADC equal to (n + m-) periods of the network, the zero level of the instrument is measured. The output code of the ADC is then determined by the expression

m,

N. K. Or 1 1

s-nd-t-)

The measured zero level offset values are also stored in memory 8 and are used when calculating the corrected measurement result.

Next are the temperature measurement cycles. At the command of the MP 9 switch 3 sequentially connects to the input of the UFD 4 thermal converters. At the same time, the output signal MP 9 establishes the correspondence of the value of the gains of the DCF and the integration time of the ADC equal to n periods of the network. The output code of the ADC. is defined as N ,, (U:,; - f U, J к. S п, where 15, is the EMF of the i-ro sensor.

According to the results of three measurements in accordance with the program z.olennogo ZU 8, MP 9 calculates the corrected measurement result using the formula

Thus, the task of forming a series of exemplary voltages, about a.x for calibrating an instrument at various coefficients of its formation, is reduced to the size of a simple task of forming exact time intervals of a desired duration. The extra time spent associated with an increase in the measurement of exemplary signals is negligible, since

N

xi

ffl in

N 1 -N / (1+ n) and (l + n) automatic instrument calibration

 in, -J-. - - - - - - --..- “- e--“ “i-“ - eeie - etab-tn TTUcr fTi y vjt ff- r-rtr ..

Kop

N,

- N

is performed once every 100–200 measurement cycles of the sensor signal. Calibrating the instrument at different measurement ranges using a single reference voltage source allows working with various types of sensors, which increases the functionality of the device. At the same time, it achieves with a significant simplification of the design of the device due to the use of a minimum number of precise and subgrade elements, which greatly simplifies the process of setting up and periodically adjusting the device during its verification.

Next, linearization of the characteristics of thermal converters is performed by calculating the temperature from the inverse characteristic of the sensor (u), approximated by a certain function, in particular a polynomial or fractional rational expression; After this result. temperature measurement is displayed on the display device 10, the coefficients of the approximating function, as well as the program for calculating the function (U), are stored in the memory 8.

Expression (1) shows that an increase in the integration time of the ADC for m network periods in the measurement cycle of the reference voltage U, leads to an increase in the conversion coefficient of the ADC by (1 + w- / n) times, equivalently multiplying the magnitude of the model voltage U by the known

coefficient

O. b)

Those. using a tunable source of exemplary signals with equivalent voltages equal to

and

i;

 and,

(Uf4.

The value t, taking the values O, 1,2, ..., is chosen from the condition of maximum proximity of the equivalent reference voltage and to the maximum value of the input signal and. at this measurement limit, i.e. the outcome of the condition

and C1 + 5d) and, .u, ().

With such a choice of the value of the reference voltage, the component error of the instrument dominates — the random error in determining the corrected result, caused by the discreteness of the ADC, is minimal.

Thus, the task of forming a series of exemplary voltages, not a.x for calibrating an instrument at different conversion ratios, is reduced to a significantly simple task of forming exact time intervals of a desired duration. The extra time involved in increasing the time of measurement of exemplary signals is, however, negligible, since

tab-tn TTUcr fTi y vjt ff- r-rtr ..

5 0 5

0

five

is performed once every 100–200 measurement cycles of the sensor signal. Calibrating the instrument at different measuring ranges using one source of reference voltage allows working with various types of sensors, which increases the functionality of the device. At the same time, a significant simplification of the device design is achieved due to the use of a minimum number of precision and sub-elements, which greatly simplifies the process of adjustment and periodic adjustment of the device during its calibration.

With a specific implementation of a digital thermometer, a K580VI53 type programmable timer can be used as a timer 6, which includes three independent sixteen-digit counters with programming their sharp operation. Like other peripheral elements of PM sets, the timer is interfaced with the MP system via data buses, addresses, and control. Formation of control code signal ADC with

a length that is a multiple of the mains voltage period, is carried out by the timer counters (set in mode 3) by dividing the reference frequency supplied to the clock inputs of the counters Tj by a predetermined factor. The coefficient of frequency division in the specified mode can take integer values lying in the range of 1-2. -one,

In order to ensure high accuracy in shaping the duration of the control signal ASCh and tawp around the range of tuning its duration, the O and 1 timer counters are switched on in series. The dividing coefficient d of such a two-stage counter is equal to the product of the coefficients of the ratio of,, and of each of the counters and lies in the range from 1 to (2 -1). The absolute error of setting the duration of the control pulse does not exceed the duration of the period of the voltage reference frequency, which is 0.5 microseconds when the frequency of the reference oscillator is equal to the maximum operating frequency of the timer counters, which is 2 MHz. .

UFD can be performed on an operational amplifier and in both cases and a “vertical” amplifier, which ensures its high input resistance. The switching of the gain factors is performed by the switch 12, and the resistance of the switch's public keys does not introduce any large error, since they are included in the feedback loop of the USCH.

The ASC includes a voltage converter in the time interval 13 and one of the counters of the programmable timer 6, which serves to convert the output pulse-width signal to the code and enter the information in the MP. The SC includes the source of the reference voltage 14, the keys 15 and 16, the integrator 17, the zero-organ 18, the trigger 19, the inverters 20 and 21, the coincidence circuit 22. The principle of the ADC is to integrate the input signal during the time interval T do the mains voltage, and further - to integrate the reference voltage up to the moment of zero output

integrator voltage. Holding the integrator in the zero state is performed by the output signal of the trigger 19, setting 18 degrees to one in the time interval between the two measurement cycles. The conversion of the informative signal T from the output of the coincidence circuit to a code is performed by the timer counter CT (mode 2) by counting the number of reference frequency pulses fed to the clock input of TI 2 over the measured time interval. A single signal from the output of the PLE with a duration T arrives at the authorizing input P 2 of the counter and starts the counting of pulses. When the resolution signal goes to the zero state, the pulse count stops and the accumulated information is stored in the counter until the next single signal arrives. At the same time, due to the internal logic circuits of the timer, the initial setting of the counter is carried out and the described conversion process is repeated. The moment of the end of the cycle of converting the pulse duration to a code is determined programmatically. For this MP, it reads the contents of the counter twice and compares these values to each other. The process is repeated cyclically until the read codes turn out to be equal to each other, which indicates that the pulse counting is completed and the counter is in the storage state of the accumulated information.

The microprocessor 9 is implemented on the basis of the MP K180 MP kit according to the standard MP controller circuit and includes a processor CPU 23 of the K580IK80 type, a clock pulse generator 2A of the K580GF24 type, a BIS of the system controller 25 of the K580BG28 type. The MP controller communicates with the rest of the device elements via data bus, address and control.

In addition, to display the measurement result on the display and to control the UFD and the switch, it is necessary to buffer the information set by the MP controller to the system data in a short time interval. Writing information to the buffer registers used for this purpose is triggered by address bus signals.

And control. In order to exchange information with BHemHVit & i devices in MP systems based on the K580 series, it is most advisable to use a BIS programmable parallel interface 26 (PLI) of the type K580, YK55, which includes three eight-bit ports that can be programmed on input or degenerate information. In FIG. 2, ports A and B are used to output the measurement result to an indication, port C to output the control signal of the UFT and KQNiMyTaTopa.

CIR: operation of the thermometer MP 9 exists Control of switch 3 for the purpose of connecting to the input of the measurement channel one of the thermocouples, the source of the reference voltage 2 or a zero signal. The control word code of the switch is stored in memory 8. JB the required time is read by MP 9 and loaded into the buffer output register. The output code of the buffer register selects one or another channel of the switch 3. Switching of the gain factors of TFC 4 is carried out by the remaining bits of the same buffer. The control signal is generated by the ADC for a duration of a network voltage, is programmed by By measuring 6 by dividing the reference clock from the output of the pulse generator 7 by the corresponding coefficient. The division factor is recorded in the memory 8 and entered into the timer 6 by U 9, Processing the measurement results, including the calculation of the corrected result after auto-calibration and linearization of the sensor characteristics, is performed by the MP 9 in accordance with the program stored in the memory 8. The overall algorithm of the device, i.e. the sequence of performing the necessary hfgh operations, is also defined by the PM 9 in accordance with the program recorded in the memory 8.

five

ten

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The measurement accuracy of the proposed device is enhanced by automatic zero correction and sensitivity. At the same time, the principle of channel calibration in a device with different conversion factors using one exemplary MejMJ allows one to make high-precision measurements using various types of thermal converters and thus increase the functionality of the device.

f o rm u l a and 3 o b e te n u

A multichannel digital thermometer containing thermoelectric converters connected to the switch inputs, one of the inputs of which is connected to the common thermometer bus, and a control input connected to the first output of the microprocessor, the input of the second one connected respectively to the output of the analog-digital converter and the output of the memory device, and The second output is connected to the display device, which is designed so that, in order to improve the measurement accuracy by ensuring the automatic calibration of the thermometer, put programmable timer, pulse generator, reference voltage source and a DC amplifier with adjustable gain, whose input is connected to the switch output, control input connected to the third output of the CPU, and output connected to the analog-digital input the converter, the control input of which is connected with the output of the programmable timer, the clock and control inputs of which are connected respectively to the pulse generator and the fourth output of the microprocessor; regular enrollment model voltage is connected to an additional input of the switch.

Compiled by V.Kulikov Redak Ohr L.Povkhan Tekhred L.Serdoykova Corrector V.Eut ha

Order: 2 77/46 Circulation: 778 Subscription of the USSR State Committee on matters of inventions and discoveries 113035, Moscow, / 5 Raushsk nab., 5

Przdazvodstvenno-polygraphic enterprise, Uzhgorod, ul, Proektna, 4

FIG. 2

Claims (1)

Claim A multichannel digital thermometer containing thermoelectric converters connected to the inputs of the switch, one of the inputs of which is connected to the common bus of the thermometer, and the control input is connected to the first output of the microprocessor, the inputs of which are connected respectively to the output of the analog-to-digital converter and the output of the storage device, and the second output connected to the indicating device, with the fact that, in order to increase the measurement accuracy by providing automatic calibration of the thermometer, it a programmable timer, an impulse generator, a reference voltage source and a constant current amplifier with a tunable gain, the input of which is connected to the switch output, the control input is connected to the third output of the microprocessor, and the output is connected to the input of an analog-to-digital converter, the control input of which is connected to programmable timer output, the clock and control inputs of which are connected respectively to the output of the pulse generator and the fourth output of the microprocessor, at m model voltage source is connected to an additional input of the switch.