METHOD AND DEVICE FOR DETERMINING THE CORROSION PROTECTION CAPACITY OF A LIQUID

Description

[0001] The invention relates to a method and a device for determining the corrosion protection capacity of a liquid according to the preamble of claims 1 and 8.

[0002] The fluid in question is primarily a machine coolant for internal combustion engines, especially marine engines. These coolants are subject to continuous aging during use, causing their corrosion protection capacity to gradually diminish. Coolants primarily serve to cool the engines and are subjected to significant stress, particularly at high operating temperatures, which can lead to the oxidation of their components, especially those responsible for corrosion protection. Therefore, coolants must be regularly tested for their corrosion protection properties.

[0003] Such a check can be carried out using complex chemical or physical analyses, by examining various individual parameters to determine whether the corrosion protection capacity is still present.

[0004] It is also known to determine the corrosion protection capacity by measuring the electrical conductivity between two electrodes immersed in the coolant. A corresponding method is described in DE 10 2015 204 717 A1. There, a fixed voltage potential is established between the electrodes in a sample or directly in the cooling circuit of a machine, and the current flowing between the electrodes is measured using an ammeter. The evaluation is performed by comparing the value of the current flowing in the coolant being measured with the value of a new coolant under identical operating parameters.

[0005] One problem with such measurements is that the electrodes used are also susceptible to corrosion, and therefore the result of a measurement, especially during continuous operation of a measuring device, can be unreliable.

[0006] From DE 10 2017 200291 A1, a method for measuring the purity of cooling water for an internal combustion engine is known, in which an energy storage device is discharged by means of two electrodes that are subjected to a DC voltage pulse, depending on the conductivity of the water. A corrosion protection capacity is derived from the discharge time between a first and a second state of charge.

[0007] From EP 0 224 323 A2, a sample container is known which has two electrodes arranged in parallel. The device can be connected to a DC voltage source and has several energy storage devices.

[0008] From EP 0 412 746 A2 a device for testing a fluid is also known, wherein the quality of the fluid is determined by measuring the conductivity of the fluid and comparing it with reference values.

[0009] The invention is therefore based on the objective of providing a method and a device for determining the corrosion protection capacity of a liquid, in particular a coolant for internal combustion engines, which allows for improved measurement accuracy, simple evaluation options and the use of simple hardware.

[0010] This problem is solved by the invention specified in claims 1 and 8. Further embodiments of the invention are specified in the dependent claims.

[0011] In the invention, two electrodes are inserted into the liquid to be evaluated. The electrodes are configured as a corrosion-prone working electrode and a corrosion-free counter electrode. A direct current voltage, derived from an energy storage device, is applied to the two electrodes. This energy storage device discharges during the measurement due to the current flow between the electrodes. The quality criterion for corrosion protection is determined either by measuring the time between a first and second charge state of the energy storage device or by measuring the charge state of the energy storage device after a defined period of time from an initial charge state.

[0012] Preferably, the energy storage device is an electrolytic capacitor that is slowly discharged by the current flow between the electrodes, and whose state of charge is determined by measuring the voltage across the terminals of the energy storage device. In a preferred embodiment of the method, a constant voltage potential is applied to the electrodes for a defined period of time in a first step to initialize them, thereby sensitizing the working electrode to corrosion. Subsequently, in a second step, the electrodes are connected to the energy storage device, which then slowly discharges due to the current flow between the electrodes. The discharge voltage is measured continuously or at fixed intervals. The measurement is terminated as soon as a defined period of time has elapsed since the electrodes were connected to the energy storage device, or when the discharge voltage reaches a preselected potential.

[0013] The device for determining corrosion protection consists of a sample container in which two electrodes are immersed parallel to each other at a small distance into a sample of the coolant. In the first step, the electrodes are connected to a constant voltage potential, and in the second step, to an energy storage device that discharges due to the current flowing through the electrodes. A control circuit is present that switches the electrodes in the second step from the voltage potential of the first step to the voltage potential of the energy storage device.

[0014] The control circuit is also designed to record, in the second step, the time period between the state of charge of the energy storage device at the beginning of the second step and the achievement of a selected voltage potential during the discharge of the energy storage device, or to record the difference between the voltage potential at the beginning of the second step and the voltage potential at the end of a certain period of discharge.

[0015] The invention makes it possible to determine characteristic properties of a deterioration in the corrosion protection capacity of a coolant even before the chemical composition and physical properties allow conclusions to be drawn about it.

[0016] The invention is explained in more detail below using an exemplary embodiment. The figures shown are: Fig. 1 a side view of a housing with a sample container, Fig. 1 a sectional view of a housing with sample container with inserted electrodes, Fig. 2 a circuit arrangement for controlling the method according to the invention, and Fig. 3 a program sequence of the device for carrying out the method.

[0017] The in the Figure 1 The housing shown in a and 1b has a wall 1 containing a heating element 9 (not shown) that surrounds a sample container inserted into the housing. Two rod-shaped electrodes 3 and 4 are anchored parallel to each other at a small distance within a sample head 2 of the sample container. Used electrodes can be removed from the sample head and are replaced with unused ones after each measurement.

[0018] To ensure measurement repeatability, defined initial conditions are established with regard to test volume, sample temperature, test specimen surface area, and exposure time. The test volume is preferably 30–50 ml, and the same test volume should be maintained for each measurement. The sample temperature should be in the upper range of the coolant's regular operating temperature, which is approximately 50–80 °C, and the temperature should be the same for each measurement, preferably 60 °C. The uniformity of the electrode test specimen surface is achieved through corresponding manufacturing specifications. The working electrode, i.e., the electrode that acquires corrosive properties during the measurement and is connected to the negative terminal of the test voltage, is replaced with a new electrode after each measurement.

[0019] Figure 2Figure 1 shows a control circuit for carrying out the method according to the invention. A central component of the control circuit is a microcomputer 5, e.g., an Arduino. This can perform the necessary process steps through appropriate programming. The control circuit is preferably located within the free space of the sample container.

[0020] In the preparation phase, a defined volume of the coolant to be tested is poured into the sample container. This is heated to the measurement temperature of 60 °C by the heating element 9. The heating and maintenance of the measurement temperature is controlled by the microcomputer 5 via a temperature sensor 6. As soon as the measurement temperature is reached, the sample head 2 with electrodes 3 and 4 is placed on the sample container so that the electrodes are immersed in the coolant to a defined length.

[0021] The first step is a reaction phase in which the electrodes are actively polarized. For this purpose, a constant voltage of approximately 1 volt is applied to electrodes 3 and 4, with the working electrode connected to the negative terminal and the counter electrode to the positive terminal of the power supply. During the reaction phase (first step), the applied voltage potential causes the working electrode to become corrosively sensitive. The release of metal ions can also accelerate the activation of potential inhibition mechanisms. The duration of the reaction phase is determined by the time required to develop surface protection on the working electrode, after which a relatively stable surface protection is achieved. This is approximately 10 minutes for a new coolant. The voltage level is below the voltage that could lead to unwanted electrolysis.

[0022] The replaceable working electrode is preferably made of copper, cast iron, brass, or an aluminum alloy and should be the same or similar to the corrosion-prone material of the cooling circuit in which the coolant circulates. The counter electrode is preferably made of a precious metal or stainless steel.

[0023] The voltage of 1 volt applied to the electrodes via terminals 7 and 8 in the first step is routed from the microcomputer 5 via transistor 10 and diode 13 to terminal 7 for the counter electrode, with the working electrode 8 connected to ground and diode 12 preventing the capacitor 11 from charging. A 20 pF capacitor 15 stabilizes the voltage in the first step.

[0024] Switching off transistor 10 terminates the first step. An electrolytic capacitor 11 is then charged by applying a charging voltage of 5 volts through the activation of transistor 14. Once the charging voltage reaches the intended initial voltage of the second step, the charging of capacitor 11 is deactivated by switching off transistor 14, and the capacitor 11 can slowly discharge via electrodes 3 and 4, which are connected to terminals 7 and 8. The capacitor preferably has a capacitance of 1 µF. While a higher capacitance would increase the discharge time, it would also increase the risk of electrolysis of the working electrode. With a capacitance of 1 µF, the measurement time is approximately 20–100 seconds, with the lower limit of the measured voltage being 0.5 volts. Diodes 16 and 13 isolate the charging circuit.

[0025] The microcomputer 5 uses internal clock counting to determine the time it takes for the voltage of capacitor 11 to drop from its initial value of 5 volts to the final value of 0.5 volts.

[0026] The duration of the voltage drop recorded for a sampled coolant is compared in tabular form with previously determined values ​​for known coolants, either manually or via suitable microcomputer programming, and displayed on a display unit (not shown). Since the discharge time of capacitor 11 depends on the corrosion protection capacity of the coolant, a longer discharge time correlates with better corrosion protection of the working electrode.

[0027] An electrolytic capacitor is preferably used. For high measurement accuracy, a tightly toleranced capacitor (≤ 5%) is advantageous. Furthermore, the voltage measurement should preferably be performed with a resolution of 10 bits, and a high input impedance of >100 MΩ should be selected.

[0028] Figure 3 The diagram illustrates the procedure once more. In step 17, the coolant sample is heated to the target temperature of 60 °C. In step 18, the holding voltage of 1 V is applied, with diode 12 preventing capacitor 11 from charging. Finally, in step 19, the holding voltage is deactivated by switching off transistor 10.

[0029] Step 20 follows, in which capacitor 11 is charged to an output voltage of 5 V via transistor 14. After capacitor 11 is charged, transistor 14 is switched off to discharge it, and in step 22 the measurement cycle is started. Capacitor 11 is discharged via terminals 7 and 8 with the electrodes connected to them. As soon as the voltage across capacitor 11 reaches the target value of the residual voltage, the measurement cycle is terminated. Reference sign

[0030] 1 Wall 2 Sample head 3 Electrode 4 Electrode 5 Microcomputer 6 Temperature sensor 7 Connection to counter electrode 8 Connection to working electrode 9 Heating element 10 Transistor 11 Capacitor 12 Diode 13 Diode 14 Transistor 15 Capacitor 16 Diode 17 Sample heating 18 Holding voltage applied 19 Holding voltage deactivated 20 Charging phase 21 Charging voltage deactivated 21 Discharge

Claims

1. A method for determining the corrosion protection capacity of a liquid, in particular of a coolant for an internal combustion engine, by means of establishing the electric conductivity between two electrodes (3, 4) introduced at a distance from one another into a sample of the liquid, wherein a DC voltage is applied between the electrodes (3, 4), characterised in that the electrodes (3, 4) are configured as a working electrode which is prone to corrosion and a corrosion-free counter electrode, and wherein the DC voltage is derived from an energy storage device (11) which discharges via the electrodes (3, 4) as a function of the conductivity of the liquid, and that the corrosion protection capacity is derived from the establishment of the length of time of the discharge between a first and a second state of charge of the energy storage device or the state of charge of the energy storage device after a specified period of time has elapsed.

2. The method according to Claim 1, characterised in that the energy storage device (11) is an electrolytic capacitor.

3. The method according to Claim 1, characterised in that the state of charge of the energy storage device (11) is determined by measuring the voltage at the poles of the energy storage device.

4. The method according to Claim 1, characterised in that a constant voltage potential is applied to the electrodes (3, 4) for a specified length of time in a first step, and that after the specified length of time has elapsed, the energy storage device (11) which is charged to an initial voltage potential discharges independently in a second step, wherein the discharge voltage of the energy storage device is measured continually or at specified times.

5. The method according to Claim 4, characterised in that the electrodes (3, 4) are connected to a voltage source with constant voltage potential in the first step, and are connected to the charged energy storage device (11) in the second step.

6. The method according to Claim 4, characterised in that a voltage of 0.5 - 1.5 volts, preferably 1 volt, is applied to the electrodes (3, 4) for a length of time of 8 - 15 minutes, preferably 10 minutes, in the first step, and that the initial voltage potential is 4.5 - 5.5 volts, preferably 5 volts.

7. The method according to one or more of the preceding claims, characterised in that the determination of the corrosion capacity of the liquid to be tested is carried out by tabular comparison of the length of time of the discharge of the energy storage device or of the discharge voltage determined after a specified length of time has elapsed with comparison values of samples of a comparison liquid known in terms of its quality.

8. A device for determining the corrosion protection capacity of a liquid for performing a method according to Claim 1, characterised in that a sample container is provided, which has electrodes (3, 4) arranged parallel to one another therein, said electrodes being configured as a working electrode which is prone to corrosion and a corrosion-free counter electrode, that a DC voltage source is provided, wherein the electrodes (3, 4) can be connected to the DC voltage source which is configured to have a constant voltage potential in a first step, that an energy storage device (11) is provided, which can be connected to the electrodes (3, 4) in a second step and which is configured to discharge via the electrodes (3, 4) immersed in a liquid to be tested, and that a control circuit (5) is provided, which is configured to switch over the electrodes (3, 4) from the voltage potential of the DC voltage source with constant voltage to the voltage potential of the energy storage device (11) in the second step, and wherein the control circuit (5) is designed to capture the length of time between the first state of charge at the start of the second step and the achievement of a second state of charge or to establish the voltage potential of the energy storage device after a specified length of time has elapsed from the start of the second step.

9. The device according to Claim 8, characterised in that the energy storage device (11) is an electrolytic capacitor which is charged by the DC voltage source with constant voltage, and that the control circuit (5) is designed to disconnect the electrolytic capacitor from the DC voltage source with constant voltage for discharging via the electrodes (3, 4) in the second step.