Basic concepts and knowledge of instrumentation

1. Classification of analytical instruments

There are many types of analytical instruments with different uses. According to the measurement principle and analysis method, analytical instruments can be roughly divided into the following categories.

(1) Electrochemical analytical instruments

Various electrochemical analytical instruments using potential, conductivity, and current analysis methods, such as zirconium oxide oxygen analyzers, fuel cell oxygen analyzers, electrochemical toxic gas detectors, etc.

(2) Thermal analytical instruments

such as thermal conductivity gas analyzers, catalytic combustion flammable gas detectors, etc.

(3) Optical analytical instruments

include infrared gas analyzers using absorption spectroscopy, near-infrared spectrometers, laser gas analyzers, ultraviolet-visible spectrophotometers, ultraviolet fluorescence analyzers, etc.

(4) Trace water analyzers

generally include electrolytic trace water analyzers, capacitive trace water analyzers, crystal oscillation trace water analyzers, cold mirror trace water analyzers, etc.

2. Analysis of basic parameters of analytical instruments

(1) The measurement range

is also called the range, which refers to the area between two extreme values ​​and is expressed by the upper and lower extreme values ​​of the quantity under consideration.

Range selection: The selection of instrument range must be clear in purpose. It should be selected according to the specific conditions and process requirements of the site, and provide the most suitable range for customers. The larger the better, it is not necessarily the better, because the error of the instrument also changes with the change of the range.

Generally, the error of our instrument is ±2%FS, that is, ±2% of the full scale. In the communication with customers, we must understand the needs of customers, especially when we encounter some customers who are not clear about the situation, and always hope that the larger the range and the higher the accuracy, the better. This requires us to do work to persuade customers to choose the most suitable one. At the same time, different ranges require different sensors. For example, trace oxygen sensors are generally better at measuring oxygen between 0-1000ppm, while constant oxygen sensors are generally used for measuring oxygen concentrations between 0.1%-80%; the range of high-purity oxygen is generally selected from 80-99.99%.

(2) Accuracy and grade

The accuracy of the instrument is also called precision, referred to as precision, which refers to the degree of consistency between the indicated value of the instrument and the true value of the measured value. The accuracy level of general instruments is level 2.
In measurement, the precision of any measurement can only be relative, and it is impossible to achieve absolute accuracy. There will always be errors caused by various reasons. In order to make the measurement results accurate and reliable, minimize errors, and improve measurement accuracy, it is necessary to fully understand the possible errors in the measurement so that necessary measures can be taken to overcome them. Usually, there are basic errors, compensation errors, absolute errors, relative errors, systematic errors, random errors, negligent errors, and sampling errors in measurement. The following explains the relative error.

① Absolute error (absolute error)

Absolute error = measurement result - (conventional) true value

② Relative error (relative error)

Relative error = absolute error / (conventional) true value

Relative error is expressed by ±%FS, FS is the abbreviation of full scale in English, and ±%FS represents the relative error of the full scale of the instrument.

Relative error of full scale of instrument = absolute error / (upper limit of measurement - lower limit of measurement) * 100%

(3) Response time and lag time of analysis

Response time is the speed of instrument measurement. It is usually defined as the time from the moment when the measured value undergoes a step change to the time when the instrument indication reaches 90% of the difference between the two steady-state values. This time is called 90% response time and is marked as T90. The lag time of

analysis is equal to the sum of "sample transmission lag time" and "analytical instrument response time", that is, the time from the sample being taken out of the process equipment to the time when the analysis result is obtained. The sample transmission lag time includes the time required for sampling, transmission and pretreatment.

(4) Stability: (stability)

Stability refers to the ability of the instrument to maintain the value of the instrument within a specified time under specified working conditions while the input remains unchanged. The stability of the analytical instrument can be characterized by two parameters: noise and drift.

Noise, also known as output fluctuation, is a fluctuation relative to the average output that is not caused by changes in the concentration of the measured component or any influencing quantity, or a random fluctuation of the output signal caused by unknown accidental factors. It interferes with the detection of useful signals.

Drift refers to the phenomenon that the analytical signal changes slowly in a certain direction. Drift includes zero drift, range drift, and baseline drift. Drift indicates the influence of system errors.

For example, the "stability: zero drift: ±1.5%FS/30d; range drift: ±1.5%FS/30d" mentioned in our instrument parameters means that the zero drift and range drift of the instrument are less than ±1.5% of the full scale (FS=full scale) after 30 days of continuous operation.

In order to improve the stability and repeatability of instruments, it is usually achieved through automatic calibration, compensation correction and other means. For example, the reference signal in the infrared gas analyzer, the double-arm bridge in the thermal conductivity sensor, and the automatic calibration in the online complete analysis system are all such means.

(5) Repeatability: (repeatability)

is also called repeatability error. It refers to the deviation between a series of results measured under the same conditions, using the same method and with the same sample. The same conditions refer to the same operator, the same instrument, the same laboratory and a short time interval.

(6) Sensitivity: (sensitivity)

refers to the change in the analytical signal when the content or concentration of the substance being measured changes by one unit, indicating the instrument's ability to respond to changes in the measured quantity.

(7) Resolution: (resolution)

refers to the instrument's ability to distinguish between adjacent signals. It is usually expressed in terms of resolution, etc. The resolution of the instrument is adjustable, and the resolution given in the instrument's performance indicators is generally the instrument's highest resolution. The higher the resolution, the lower the sensitivity.

3. Unit conversion

3.1 Pressure unit conversion table

3.2 Conversion between concentration unit ppm and mg/m3

mg/m3=M/22.4 * ppm * [273/(273+T)] * (Ba/101325)

M----gas molecular weight
ppm----measured volume concentration value
T----temperature
Ba----pressure
22.4----volume per mole of gas at 20℃ and 101.325kPa, L

4. Naming and classification of our company's products (GES-green sublimation)

(1) GES-O2 oxygen analyzer Oxygen (oxygen concentration measurement)
(2) GES-DP dew point analyzer Dew point (dew point measurement)
(3) GES-H2 thermal conductivity analyzer Hydrogen (measurement component + principle)
(4) GES-CO infrared analyzer Carbon monoxide (measurement component + principle)
(5) Alarm/handheld device (alarm, detector, focusing on qualitative analysis)
(6) Green energy gas complete analysis system (unattended online monitoring system) (end)