CN2080671U - pH meter with two-button operation - Google Patents

Abstract

A pH meter with a microcomputer for measuring the acidity of a solution. It consists of pH electrode, impedance converter, amplifier, temperature sensor, analog switch, analog-to-digital converter, microcomputer, operation switch and indicator. Its structural feature is that it can measure parameters such as electrode potential (mV), solution pH value and temperature with only two operation buttons, and can realize automatic compensation of temperature, electrode and standard buffer solution; eight light-emitting diodes are used to indicate eight types of instruments. working status. The advantages of this instrument are intelligence, high precision, simple structure, stable and reliable operation, convenient operation, low cost, and easy popularization and application.

Description

Acidimeter operated by two keys

The invention belongs to the surveying instrument to solution acidity (pH value).

The PH meter of measuring solution acidity is widely used in fields such as chemical industry, medical treatment, biology, environmental protection.Intelligent PH meter is the upgraded product of conventional P H meter.The system controlled by computer metering circuit is sampled to temperature and PH electrode potential, tries to achieve correction factor with numerical evaluation again and compensates automatically.Saved manual temperature compensation, electrode slope and three regulator potentiometers of demarcation, made that instrument calibration process and measurement are comparatively convenient, and automatic spell-checking facility is arranged.Prior art can be measured pH value and with the instrument of microcomputer two classes be arranged: a class is to survey pH value, claims PH meter; Another kind of title ionometer can also be measured multivalent ion concentration except that can measuring pH value.But the PH meter is usually with the keyswitch more than four, at least tens of ionometer buttons, operating switch is many, reliability is low, complex structure, the cost height, and during ion instrumentation pH value, the standard buffer solution pH value of calibration is input to numerical value in the instrument by keyboard after needing manually to table look-up according to solution temperature, inconvenient operation, for example the 811 type PH of Olin Corp (ORION RESEARCH INCORPORATED) count, but its potential electrode current potential, pH value, temperature, electrode conversion ratio (slope), but the function switch of regular use has adopted the many thumbwheel switches in contact, shorter than single contact switch life, poor reliability; And this instrument adopts two single chip microcomputers, and respectively electrode potential and temperature is sampled with two analog to digital converters (ADC), and is with this circuit structure complexity, with high costs.

The purpose of the invention is to manufacture and design a kind of employing a slice single chip microcomputer and a small amount of peripheral circuit, and the PH meter of two operation push-buttons is only arranged, and it can finish the function that prior art need adopt a plurality of operating switchs, complicated circuit to realize.Reduce button and make that instrument reliability improves, circuit structure is simple, easy to operate.

The main contents of the invention organization plan: the current potential of the PH electrode that will contact 1 output with solution through impedance transformer 2 and amplifier 3,4 output voltages to analog switch 7; The current signal of temperature sensor 5 outputs is also sent into analog switch 7 through amplifier 6; Only need then by two buttons 10,11 of operation, single chip microcomputer circuit 9 need to select the parameter (comprising mv value, pH value, temperature) of test to measure by the specific program control analog switch of finishing 7.Convert simulating signal to digital signal through analog to digital converter 8, again the binary-coded decimal of converter output is changed and numerical evaluation through single chip microcomputer, and with scan mode test result is presented on the charactron 12, for the stable case of the duty of instrument and the data of surveying by function and status displays 13 demonstrations.The present invention adopts 8 kinds of duties of 8 LEDs (13b) indicating instrument.

The organization plan that invention will be further ex-plained with reference to the appended drawings creates:

Fig. 1 is the general structure block scheme of the invention PH meter.Fig. 2 is a multichannel analog to digital converter basic circuit diagram.Fig. 3 is a single chip microcomputer basic structure synoptic diagram.Fig. 4 is this PH meter profile schematic perspective view.Fig. 5 is PH meter rear panel synoptic diagram, symbolic significance is among the figure: 1---the PH electrode, 2---impedance transformer, 3---amplifier, 4---amplifier, 5---semiconductor temperature sensor, 6---amplifier, 7---analog switch, 8---analog to digital converter, 9---the single chip microcomputer circuit, wherein 9a is 8031 CPU, 9b is latch 74LS373,9c is read-only memory 2732 EPROM, 9d is EingangsAusgangsSchnittstelle 8255 A able to programme, 10---function key, 11---key is set, 12---nixie display, wherein 12a is driving circuit 74LS06,12b is four seven segment digital tubes, 13---function and status displays, wherein 13a is 3-8 code translator 74LS138,13b is eight LED light emitting diodes, the NPN triode that 13c shows for the promotion state, 13d is a LED light emitting diode, 14---tool housing, 15---PH glass electrode socket, 16---PH contrast electrode binding post, 17---the temp probe socket, 18---fuse box, 19---supply socket.

As shown in Figure 1, the current potential of PH electrode 1 output is given analog switch 7 through impedance transformer 2, amplifier 3 and the voltage of the different requirements of the amplifier 4 various test parameters of output; The current signal of semiconductor temperature sensor 5 outputs also is input to analog switch 7 through amplifier 6.Making 8031 single-chip microcomputers, 9 follow procedures require to control analog switch 7 through function key 10 or operation that key 11 is set measures to select the parameter of being surveyed, convert simulating signal to digital signal through analog to digital converter 8, binary-coded decimal with analog to digital converter output carries out data processing through single-chip microcomputer 9 again, and the result is presented on 4 LED charactron 12b, but by the stable case of function and status displays 13 indicating instrument duties and measurement data with scan mode.

According to shown in Figure 2, can clearly demonstrate the circuit theory of multichannel analog to digital converter.The current potential of PH electrode 1 output is earlier through impedance transformer 2(CA3140 high resistance operating amplifier) output potential is resolution 1mV shelves signals, be input to operational amplifier (LM747) 3 and 4 respectively by the voltage of impedance transformer output and carry out voltage amplification, measure the shelves signal as resolution 0.1mV shelves and pH value and import analog switch 7(CD4051 respectively) 14 pin and 13 pin.Semiconductor temperature sensor 5(AD590) Shu Chu current signal is through I/V converter 6(LM741 operational amplifier) as temperature measurement signal, this signal is transported to 15 pin of analog switch 7.1,5 pin of analog switch 7 connect reference voltage, 2,4 pin ground connection, as the normal voltage of self check analog to digital converter input.Analog switch 7 is subjected to single-chip microcomputer 9a(8031) P _1.5, P _1.6And P _1.7The control of pin can be selected the measurement of PH, 0.1mV, 1mV and all parameters of temperature, analog switch 7 and a slice high-precision adc 8(5G1443) be connected, can realize the measurement of multiple parameters.

The full journey of the work of analog to digital converter 8 is ± 1999mV that resolution is ± 1mV.The enlargement factor of impedance transformer 2 is 1, thus from its output the direct input analog-to-digital converter 8 of voltage, its measurement range is ± 1999 ± 1mV; And amplifier 3 voltage amplification factors are 10 times, so its measurement range becomes ± 199.9 ± 0.1mV; About 4 times of amplifier 4 voltage amplification factors.Measure pH value for the dynamic range that makes full use of this analog to digital converter, the analog-to-digital conversion definition of pH value reaches ± 0.005PH.I/V converter 6 output voltages are 10mV/ ℃, and its measurement range is limited by temperature sensor, and we adopt 0～100 ℃ of the temperature range that is fit to the PH electrode at present, and resolution is 0.1 ℃.

The key character of this instrument adopts two operating keys, wherein key 10 for function key, be used for conversion and select each test parameter etc.: comprise that (this instrument has PH for the demarcation of clock, electrode potential (mV) measurement, temperature survey, electrode slope and corresponding various standard buffer solutions and measurement ₂, PH ₄, PH ₇And PH ₉Four kinds of standard buffer solutions) have eight kinds of duties, by eight corresponding states of LED light emitting diode indication; Another key 11 claims key is set, and is used to be provided with clock, manual temperature compensation setting, manually temperature value setting during temperature compensation, and to certain selected standard buffer solution a bit or two-point calibration start and delete a certain point of having calibrated.

Above-mentioned standard buffer solution pH value temperature influence, this instrument adopts four kinds of standard P H buffer solution, is 0.05M four potassium binoxalate, 0.05M Potassium Hydrogen Phthalate, 0.025M mixed phosphate and 0.01M borax.These four kinds of buffer solution are corresponding to PH ₂, PH ₄, PH ₇And PH ₉Four scaling points, the user can choose one or both buffer solution arbitrarily and calibrate, and claims also a bit or two-point calibration that the pH value of damping fluid and variation of temperature relation all deposit in the microcomputer.When calibration,, revise the pH value of selected standard buffer solution automatically by microcomputer according to the survey solution temperature.

As shown in Figure 3, microcomputer 9 adopts the chip of MCS51 series, and it is by single-chip microcomputer (8031) 9a, latch (74LS373) 9b, reservoir EPROM(2732) compositions such as 9c and programmable interface chip (PIO 8255A) 9d.Micro-architecture is simply compact, the P by 8255 and 8031 ₁Required IO interface such as the existing multichannel analog to digital conversion control of cause for gossip, keyboard interface, demonstration output interface.All softwares (about 3.8KB) are solidificated in the EPROM2732 4KB capacity 9c.Obtain digital signal from analog to digital converter 8, after single-chip data is handled, pass through 8255 A mouth and last half C mouth, promote LED charactron 12b display result through driver (74LS06) 12a again.8255 B mouth links to each other with analog to digital converter (5G14433) 8.8255 times half C mouth is used for function and state demonstration by 13a, 13b, 13c and 13d, wherein three output to code translator (74LS138) 13a, light 8 LED13b respectively and indicate Instrument working state at that time, also has one by a NPN triode 13c amplification, drive LED13d indication measurement stable case as a result, after display result is stable, promptly lighted, reliable results this moment is described. Button 10,11 is connected the P of single-chip microcomputer 8031 _1.0And P _1.1Pin.

The surface of tool housing 14 shown in Figure 4 is equipped with eight LED light emitting diode 13b, light emitting diode 13d, four seven segment digital tubes 12b and function keys 10 and key 11 is set; Member such as circuit and single chip microcomputer all is contained in this shell.

PH glass electrode socket 15 shown in Figure 5 all is connected with PH electrode 1 with PH contrast electrode binding post 16, and the temp probe socket links to each other with semiconductor temperature sensor 5.

The microcomputer that this instrument adopts is take MCS 51 series monolithics of high integration as core, in addition new periphery circuit design. Make this product have simple in structure, hardware component is few, cost is low, the characteristics of reliable operation. Adopt a slice high precision analogue converter ic to measure mV, pH value and temperature, take full advantage of analog-digital converter dynamic range measurement pH value, make the accuracy of instrument height, the operation scheme of two keys of employing is finished the auto-compensation of parameter measurement and temperature, electrode and standard buffer solution, makes instrumentation very convenient. According to the invention scheme made that function is strong, intelligent, easy to operate, working stability, with low cost, PH meter that precision is high.

Claims (2)

1. A pH meter with a microcomputer for measuring solution acidity, comprising a pH electrode, an impedance converter, an amplifier, a temperature sensor, an analog switch, an analog-to-digital converter, a microcomputer, an operation switch and an indicator, and is characterized in that there are only two One operation button, i.e. function key [10] and setting key [11], uses 8 light-emitting diodes LED (13b) to indicate 8 kinds of working states of the instrument. 2. The acidity meter for measuring solutions according to claim 1, characterized in that the microcomputer is composed of a single chip microcomputer 8031 (9a), a latch 74LS373 (9b), a storage EPROM2732 (9c) and a programmable interface chip PIO 8255A (9d) It consists of multi-channel analog-to-digital conversion control, keyboard interface and display output interface through the _P1 port of 8255 and 8031. All software is solidified in EPROM2732 4KB capacity (9c), and the digital signal is output from the analog-to-digital converter (8). After data processing of the single chip microcomputer, the A port and the upper half of the C port of the 8255 are passed, and then the driver 74LS06 (12a) drives the LED digital tube (12b) to display the result. The three bits of half of the C port are output to the decoder 74LS138 (13a), and 8 LEDs (13b) are respectively lit to indicate the working status of the instrument at that time, and one bit is amplified by an NPN transistor (13c) to drive an LED (13d) To indicate the stability of the measurement results, the keys [10] and [11] are respectively connected to pins P _1.0 and P _1.1 of the single-chip microcomputer 8031.

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