How to Troubleshoot Single Beam Instability of colorimeter?

Ideas and methods to eliminate unstable faults

The Colorimeter is one of the common analytical instruments and is widely used. Instability of indication value is also a common fault encountered by instrument users and testing personnel. For the colorimeter, “instability of the indication value” means that after the instrument is fully warmed up, the maximum change of the instrument’s indication value within three minutes under both the photoelectric conversion element is not receiving light or receiving light exceeds the technical specification requirements (except environmental factors). Because there are many factors that cause the instability of the indicator value, many inspection and maintenance personnel are very confused when troubleshooting and cannot start. If we can understand the working principle of the colorimeter, understand its internal structure and carefully analyze the unstable failure phenomenon of the instrument, we can determine the cause of the instrument failure and find a breakthrough to eliminate the instrument failure.

According to the optical path and circuit structure of the colorimeter, we know that the colorimeter finally indicates the energy of light. As long as the intensity of the light irradiated on the photoelectric conversion element changes, the magnitude of the indicated value changes, and the unstable operation of the signal amplifier circuit itself will also lead to the unstable output. Therefore, there are two kinds of unstable failures of the portable colorimeter: (1) Photoelectric conversion. The element is unstable when exposed to light (commonly referred to as bright current instability). (2) The photoelectric conversion element is unstable when it is not exposed to light (usually referred to as dark current instability).

The optical path and circuit structure of the colorimeter

The effective method is to use the exclusion method. The essence of the exclusion method is to achieve the purpose of narrowing the fault range through observation-judgment-verification, and can accurately find the breakthrough of the unstable failure of the instrument. The observation process should be careful, especially the accumulation of experience. For example, if the instrument is unstable, the value is drifting upwards or downwards, whether it is an instantaneous jump or a slow change, whether it is jumping up and down, whether the amplitude of the up and down jump is large, and so on. These are an important basis for judging the cause of the failure. Judgment is to eliminate the factors irrelevant to the instability of the instrument and determine the factors that cause the instability of the instrument. Verification is the further confirmation of the observation and judgment, and it is also the specific work of eliminating the unstable failure of the instrument. The verification work must be scientific, in line with relevant principles, and be simple and easy to implement.

Analysis and Troubleshooting of colorimeter Single Beam Instability Failure

The instability of the colorimeter when its photoelectric conversion element is not exposed to light has nothing to do with the optical path factor. Therefore, the unstable failure of the instrument mainly has the following factors:

  • The photoelectric conversion components are of poor quality, damp, poor contact, etc. This kind of failure is more common when the instrument has a long service life or is not used for a long time.
  • The positive and negative power supplies to the signal amplifier are unstable. The main factor is the insufficient capacitance of the filter capacitor in the voltage regulator circuit. The pressure adjustment potentiometer is in poor contact or the performance of the adjustment tube is not good.

Remedy: Use a digital multimeter to measure whether the positive and negative power supply voltages are stable. If necessary, replace the above components one by one.

  • The Signal amplifier performance is not good. The main factors are the poor insulation of the signal amplifier circuit board due to moisture, the poor performance of the integrated amplifier circuit, the poor contact of the zero adjustment potentiometer, and the poor contact of the magnification selection switch.
Causes of poor insulation of the signal amplifier circuit board

The methods of exclusion: Clean the circuit board and dry it; replace the integrated amplifier circuit; slowly adjust the potentiometer to see if there is a jumping word or needle; replace the potentiometer; switch the selector switch repeatedly to observe the repeatability of the instrument; replace the switch.

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