JPS6212860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring solution conductivity.

When a solution conductivity detector is installed on-site (transmitting side) and the detection signal of this detector is transmitted to an indicator or recorder on the receiving side installed at a remote location, conventionally, the distance between the transmitting side and the receiving side is four-way. Connected by a wire transmission line, two wires of which supply the operating power of the transmitting circuit from the receiving side, and the other two wires transmit the detection signal from the transmitting side to the receiving side. is the most commonly used, but the line configuration is unavoidably complicated.

For this reason, a proposal has been made to simplify the line configuration by connecting the transmitting side and the receiving side with a two-wire transmission line, which is used for both supplying operating power and transmitting detection signals. Since there is no DC insulation between the input and output of the circuit, it is impossible to ground each circuit on the transmitting side and the receiving side independently, and therefore it is difficult to operate each circuit stably.

The present invention connects the transmitting side and the receiving side with a two-wire transmission line, which is used for both supplying operating power and transmitting detection signals, simplifying the line configuration, and connecting the input and output of the transmitting side circuit with a two-wire transmission line. The purpose of the present invention is to realize a solution conductivity measuring device that can stabilize operation by separately grounding each circuit on the transmitting side and the receiving side by insulating the circuits.

The figure shows an embodiment of the present invention, in which Q1 is an operational amplifier forming a rectangular wave oscillation circuit, Q2 is a field effect transistor, Z1 is a Zener diode, and C
1 is a DC blocking capacitor, Q3 is an operational amplifier for impedance conversion, and CE is a cell for measuring conductivity, in which an electrode for measuring the conductivity of the liquid to be measured is provided. Q4 is an operational amplifier for AC amplification, T1 is an isolation transformer, Q5 is an operational amplifier forming a rectifier circuit such as an idealized diode circuit, R1 and C2 are resistors and capacitors forming filter F, and Q6 is a temperature compensation circuit. A temperature compensation element (for example, a thermistor) RT inserted into the feedback circuit of the operational amplifier formed is installed in the conductivity measurement cell CE. Q7 is transistor Q8 and Q9
Z2 is a Zener diode, Q10 is a starting field effect transistor, RS is a variable resistor for span adjustment, RZ is a variable resistor for zero adjustment, RF is a feedback resistor,
RC is a calculation resistor, R2 and R3 are voltage dividing resistors, Q1
1 is an operational amplifier forming an adder circuit, Q12 and Q13 are inverters forming an oscillation circuit, Q14
is a buffer inverter, T2 is an isolation transformer,
D1, D2 and D3 are rectifying elements, C3 to C5
is a smoothing capacitor, +E1 and +E2 are positive operating voltage supply terminals, -E1 and -E2 are negative operating voltage supply terminals, L is a two-wire transmission line, ES is a DC power supply, and RD is a receiving device for indicating or recording. Consists of total. In addition, operational amplifiers Q1, Q3 to Q7 and Q
11 is formed using, for example, a micropower operational amplifier with low power consumption, and inverters Q12 to Q14 are formed using, for example, CMOS inverters.

When the receiving side DC power supply ES is connected to the transmitting side circuit via the line L, the regulated positive working voltage is taken out from the terminal +E2 connected to one end of the Zener diode Z2, and the primary winding of the isolation transformer T2 A negative side operating voltage obtained by rectifying the line current with the rectifying element D1 is taken out from the terminal -E2. This operating voltage activates an oscillation circuit consisting of inverters Q12 and Q13, and its oscillation output is applied to the primary winding of isolation transformer T2 via buffer inverter Q14, and the secondary output is applied to rectifiers D2 and D3 as well as It is rectified and smoothed by smoothing capacitors C4 and C5, and taken out as positive and negative operating voltages from terminals +E1 and -E1. This operating voltage causes an oscillation circuit consisting of operational amplifier Q1 to oscillate, and its rectangular wave oscillation output is applied to the gate of field effect transistor Q2, causing the constant voltage of Zener diode Z1 to be interrupted by Q2. Therefore, a stable half-wave rectangular wave signal with an amplitude equal to the period of the oscillation output of the operational amplifier Q1 is extracted from the drain and source of the field effect transistor Q2, and is passed through the DC blocking capacitor C1 and the impedance conversion operational amplifier Q3. is added to the electrode of the conductivity measurement cell CE. The AC output of operational amplifier Q4 is connected to cell CE.
The conductivity of the liquid to be measured is proportional to the conductivity of the liquid to be measured interposed between the electrodes installed in the , and is rectified by being applied to a rectifier circuit consisting of an operational amplifier Q5 via an isolation transformer T1. After compensating for changes in conductivity due to temperature changes in the liquid to be measured, it is applied to the base of transistor Q9 via variable resistor RS for span adjustment, operational amplifier Q7, and transistor Q8. . Therefore, the collector current of the transistor Q9, that is, the current flowing through the transmission line L, changes depending on the output voltage of the operational amplifier Q7, and the conductivity of the liquid to be measured is indicated or recorded by the receiving device RD or by the recorder. .

By adjusting the span adjustment variable resistor RS and the zero adjustment variable resistor RZ, it is possible to limit the change in the current of the line L corresponding to the change in the conductivity of the liquid to be measured to a range of, for example, 4 mA to 20 mA.

Note that the voltage drop across the feedback resistor RF inserted in the collector circuit of the transistor Q9 is negatively fed back to the non-inverting input terminal of the operational amplifier Q7 via the operational resistor RC, so that the voltage/current conversion operation is performed extremely stably.

In addition, the operating voltages of terminals +E1 and -E1 vary in proportion to the resistance value of the liquid to be measured in the measurement cell CE. For example, when the resistance value of the liquid to be measured is low, the voltages of terminals +E1 and -E1 also change. I try to go down, but
In this case, the collector current of the transistor Q9 increases and the voltage drop across the feedback resistor RF becomes large, and this voltage drop is divided between the voltage divided by the voltage dividing resistors R2 and R3, that is, the voltage divided by the voltage at the terminal +E2, and the operational amplifier Q11. Added to inverters Q12 and Q13
Since the voltage is supplied as the operating voltage of the oscillation circuit consisting of the oscillator circuit and operates to increase the voltages of the terminals +E1 and -E1, accurate measurement is always possible regardless of the resistance value of the liquid to be measured.

The input/output relationship in the device of the present invention is expressed numerically as follows.

Io=1/RF(K・E1/CRC/RSRT・K+E2
/RZ) However, Io: Current in line L RF: Resistance value of feedback resistor RF K: Constant E: Output voltage of operational amplifier Q3 C: Cell constant of measurement cell CE RC: Resistance value of operational resistor RC RS: Span Resistance value of variable resistor RS for adjustment RT: Resistance value of temperature compensation element RT K: Conductivity of liquid to be measured E2: Operating voltage of terminal + E2 RZ: Resistance value of variable resistor RZ for zero adjustment As is clear from the above explanation In addition, the present invention simplifies the line configuration by using a two-wire transmission line for both supplying operating power and transmitting detection signals, and also provides direct current isolation between input and output on the transmitting side using an isolation transformer. This makes it possible to stabilize the operation by separately grounding the transmitter and receiver circuits, and also to change the oscillation output voltage of the oscillation circuit consisting of inverters Q12 and Q13 according to the resistance value of the liquid to be measured. Therefore, the operating voltage of the resistance value (i.e., conductivity) measurement circuit of the liquid to be measured is held constant to ensure accurate measurement at all times, which is extremely effective.

[Brief explanation of the drawing]

The figure shows one embodiment of the present invention, and Q1, Q
3 to Q7 and Q11: operational amplifier, Q2 and Q10: field effect transistor, Z1 and Z2:
Zener diode, C1 to C5: capacitor, CE: conductivity measurement cell, T1 and T2: isolation transformer, R1 to R3: resistor, RT: temperature compensation element, Q8 and Q9: transistor, RS and
RZ: variable resistor, RF: feedback resistor, RC: operational resistor, Q12 to Q14: inverter, D1 to D3: rectifier, +E1, -E1, +E2 and -
E2: Operating voltage supply terminal, L: Transmission line, ES:
DC power supply, RD: Receiving device.

Claims (1)

[Claims] 1. A first oscillation circuit that applies an output to a conductivity measurement electrode installed in a solution conductivity measurement cell, and an AC amplifier that sends out an output corresponding to the conductivity of the liquid to be measured interposed between the conductivity measurement electrodes. a rectifier circuit into which the output of the AC amplifier is introduced via a first isolation transformer; a voltage/current conversion circuit into which the output of the rectification circuit is introduced via a temperature compensation circuit; a two-wire transmission line connecting in series a receiving device consisting of an indicator or recorder and a DC power supply on the output side; a second oscillation circuit;
The voltage across the Zener diode inserted on the output side of the current conversion circuit is converted into the rectifier circuit, the temperature compensation circuit,
A circuit that supplies a positive operating voltage to a voltage/current conversion circuit and a second oscillation circuit, and operation of the second oscillation circuit in response to a voltage drop across a resistor inserted on the output side of the voltage/current conversion circuit. a circuit for controlling voltage; a second isolation transformer to which the output of the second oscillation circuit is applied; and a circuit for rectifying the primary winding current of the second isolation transformer to connect the rectifier circuit, temperature compensation circuit, voltage/current A circuit that supplies the negative side operating voltage of the conversion circuit and the second oscillation circuit, and a circuit that rectifies the secondary side output of the second isolation transformer for each positive and negative polarity to supply the positive and negative operating voltage of the first oscillation circuit and the AC amplifier. A solution conductivity measurement device characterized by comprising a circuit for supplying an operating voltage.