Calorimeter, Colorimeter, or Color Tester Device

The purpose of color measurement testing is to provide a method for measuring the color of petroleum products in accordance with ASTM D1500. The color tester device measures based on color spectrum rather than wavelength, covering a wide range of petroleum products such as lubricating oils, heat transfer oils, diesel fuels, and petroleum waxes.

Determining the color of petroleum products is mainly used for control purposes. Since the color of a sample is easily observed by the buyer of the product, it is considered an important quality characteristic. In some cases, the color of a sample may indicate the degree of refining of petroleum materials. When the range of color for a sample or specific products is known, if the sample’s color falls outside that range, it may indicate contamination with other products.

However, color alone should not be considered a fully reliable guide for product quality control and should not be used without considering other characteristics of the final product. In the simplest method, the sample’s color is compared to a series of colored glass plates, graded from 0.5 to 8. If the color of the sample does not exactly match one of the reference plates and falls between two standard colors, the higher grade is reported.

Terminology and Definitions in Colorimetry Testing

Sampling should be carried out according to Iranian National Standard №4189. For diluents, kerosene with a lighter color than +21 on the Saybolt scale (as measured by Iranian Standard №2932) or lower than 1.5 on the IP17 — Method B scale should be used to dilute dark samples. If the kerosene color is lighter than a potassium dichromate solution prepared by dissolving 4.8 mg of pure dichromate in one liter of distilled water, the solvent can be used as a diluent.

Calibration of the device should be performed at least once a year using a certified reference material (CRM), which may be colorless paraffin or a Merck reference.

Safety Precautions

The colorimeter should be placed on a leveled laboratory bench, and the adjustable base should be used for proper leveling. The power cable must be connected directly to a reliable wall socket and not to weak or non-standard power strips. During startup, the device consumes up to 5 amperes of current, so the wiring and connections must be secure. The supplied high-quality power cable should not be replaced with an inferior one. The distance between the back of the device and the wall should be at least 20 cm. No items should be placed on top of the device. It is preferable to keep the device under or near a laboratory hood.

In case of malfunction, users should not attempt to service or repair the device themselves. Unauthorized repairs void the warranty and after-sales service. The security seal on the D1500 device should never be broken, as this also voids the warranty. Each unit has a unique serial number, and in case of issues, users should contact the company’s support lines.

Starting the Device

Simply connect the power cable to the socket at the back of the device. By pressing the power button, the main menu will appear.

Sample Preparation for Color Testing

For liquid petroleum products such as lubricating oils, fill the sample container to a depth of at least 50 mm and observe the color in the device. If the sample is not transparent, heat it to 6°C above its cloud point according to National Standard №5438, then observe the color. If the sample is darker than color grade 8, mix 15 parts of the sample with 85 parts of kerosene and observe the mixture’s color.

For petroleum wax, petroleum jelly, or Vaseline, heat the sample 11 to 17°C above its congealing point according to ASTM D938, then test the sample at that temperature. If the color is darker than grade 8, mix 15 parts of melted sample with 85 parts of kerosene and determine the color.

Performing the Test

Pour the prepared sample solution into the glass jar up to the marked line. After cleaning the outer surface, place the cup inside the device. By pressing the start button, the color number will be displayed on the screen.

Cleaning and Reporting

Use industrial-grade solvents capable of cleaning the sample container and cap, then dry them. Toluene and acetone are commonly used solvents.

Report the color of the sample based on the closest standard reference number, for example ASTM Color = 7.5. If the color falls between two reference plates, report it as “lighter than” the darker one using the letter L, for example ASTM Color = L7.5. Never report the color as darker than the darkest reference plate, except in the case of grade 8, where darker shades may be reported as D8. If the sample was diluted with kerosene, add the abbreviation “DIL” after the reported color number, for example ASTM Color = L7.5 DIL.

Repeatability and Reproducibility

Repeatability means the difference between successive test results obtained by the same operator under the same conditions should not exceed 0.5 color units in more than one out of twenty cases. Reproducibility means the difference between independent results obtained by two operators in different laboratories with the same materials and equipment should not exceed 1 color unit in more than one out of twenty cases. No bias exists in this method since color values are inherently linked to the material and can only be determined within the method’s defined range.

Common Errors and Solutions

If the device does not turn on despite being connected to power, check the fuse located under the power cable slot. If it is damaged, replace it with the spare fuse provided. The fuse is a 15-amp glass type. If the device shows incorrect values, even with colorless paraffin, it means the device is out of calibration and must be recalibrated.

Calibration Method

In the main menu, a number appears in parentheses next to “System Standby.” This number should be adjusted based on the reference material, such as Merck standard or pure paraffin. To access calibration mode, press and hold the Start button immediately after turning on the device.

Adjust the reference sample to match the value displayed. For example, if the number in parentheses is 170 and the device shows 0.5 instead of 0 when testing pure paraffin, reduce the reference value by about 5 units until the device displays zero.

Summary of Color Testing According to ASTM D1500

Measuring the color of petroleum products requires a standardized method, internationally known as ASTM D1500. For domestic industry use, this standard has been translated and codified as INSO 203. Determining product quality is one of the main purposes of color testing, covering a wide range of products such as lubricating oils, heat transfer oils, diesel fuels, petroleum waxes, and similar materials. The light source, sample container, and a series of colored glass plates are the most important equipment required for the test. The glass plates, graded from 0.5 to 8.0, serve as the scale for measurement.

Color testers vary from highly automated devices with precision sensors to fully manual devices dependent on the operator. In manual devices, the user compares the sample color with reference plates through a viewing aperture. The sample container should be a transparent cylindrical glass tube with a flat bottom, an internal diameter of 30–33.4 mm, a height of 115–125 mm, and a wall thickness not exceeding 1.6 mm.

Further Information on Colorimeters

As mentioned, a colorimeter consists of a light source, standardized color plates, a sample holder with a cap, and a viewing aperture. In manual devices, both the sample and reference colors should be visible simultaneously. Observation may be done with or without a magnifying lens. Some manual devices have three slots for placing two standard plates, which increases accuracy. In two-slot devices, two equally bright symmetrical areas are viewed, one showing the reference color and the other showing the transmitted light through the sample.

These areas should be positioned symmetrically along a vertical axis and distinguishable along the horizontal axis, with viewing angles between 2 and 3.6 degrees. In three-slot devices, three illuminated fields are visible: two showing different reference colors and the third showing the transmitted light of the sample, with the two reference areas symmetrically placed on either side of the sample’s field.

source: دستگاه تست رنگ سنجی