How to check antifreeze with a refractometer?
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Working principle and classification
A refractometer works on the principle of refraction: when light rays pass from one liquid medium to another, they bend at different angles to the normal line between the two media. The angle of refraction depends on the composition of the medium and on the temperature. As the concentration of a particular compound in a solution increases, so does the degree of bending of the light beam. The measure of this refraction determines the physical properties of the liquid, in particular, its density. Liquids that are denser than water (have a higher specific gravity) tend to bend light through a prism more intensely than liquids of lower density. Typically, such testing is carried out under certain thermal conditions, since temperature significantly affects the angle of refraction.
When servicing a car, it is important to measure the freezing point of the engine coolant, especially after it has been mixed with water. An antifreeze refractometer helps determine the quality of the coolant. Given that the right antifreeze composition remains in liquid form even in very cold weather, the engine will always be reliably protected.
Refractometers are classified according to two characteristics:
- According to the method of counting the measurement results. Instruments of digital and analog types are produced. In the first, the desired indicator is displayed on the display screen, in the second, the measurement result is taken on a digital scale. Antifreeze refractometers are predominantly of the analog type: they are much cheaper and more compact, and ultra-high reading accuracy is not required in most cases.
- By appointment. There are medical and technical refractometers. Medical devices are specialized devices, while technical ones are more universal: in a car service, for example, they can be used not only to determine the quality of antifreeze, but also to assess the density of electrolyte in batteries.
There are also stationary and mobile refractometers. Devices of stationary action resemble a microscope in appearance, and are supplied complete with scales. The balance is calibrated to read the desired parameter value, which simplifies the measurement process.
Refractometer device and preparation for work
The device consists of the following parts:
- Durable plastic housing.
- The actual refractometer.
- Cleaning wipes.
- A set of suction tubes (usually three)
- Calibrating screwdriver.
The versatility of the refractometer is ensured by the ability to perform the following measurements:
- Measuring the freezing point temperature of automotive antifreeze based on ethylene glycol or propylene glycol.
- Determining the specific gravity of battery acid and obtaining operational information about the state of charge of the battery.
- Measuring the composition of an ethanol or isopropyl alcohol based fluid used as a windshield washer.
Reading of indications is made on scales, each of which is intended for a certain type of liquid. The antifreeze refractometer needs to be calibrated before the first use. For this purpose, tap water is used, for which the scale indicator should be at 0.
How to use an optical refractometer?
The sequence of actions to be taken depends on the type of refractometer. When using an analog refractometer, the sample is placed on a cover and prism, and then held in the light to view the scale, which is located inside the case.
Digital refractometers require that a drop of the test solution be placed in a special well. This borehole is illuminated by a light source, usually an LED, and the measuring device interprets the light transmission into a refractive index or whatever unit the instrument has programmed to read.
To obtain a result, it is enough to place 2...4 drops of the investigated liquid into the prism or well and fix the cover - this will improve the measurement accuracy, since the liquid will be more evenly distributed over the prism. Then (for an optical instrument) point the prism section of the refractometer at the light source, and focus the eyepiece until the scale is clearly visible.
The scale is read at the point where the dark and light areas meet. For a digital refractometer, the desired result is displayed after a few seconds on the display screen.
The reference temperature for measurements is 200C, although automatic compensation is designed for the range 0...300C. The length of the refractometer does not exceed 160 ... 200 mm. It should be kept dry and clean.
An antifreeze refractometer is suitable for determining the concentration of lubricating oils if their refractive indices are within the technological range of this device. To do this, a Brix diagram is preliminarily prepared and the obtained values are converted into an indicator of the density of the measured medium.
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