Introduction to the working principle of SHAW dew point meter and the use of SADP dew point meter

The working principle and method of the Xiao's dew point meter are as follows:

Because the dew point meter uses gain return, zero point automatic calibration, temperature and humidity sensor three patented technologies, the dew point meter can accurately measure the relative humidity and calculate the corresponding dew point in the environment of low humidity or corrosive chemical gas molecules. . When measuring dew points above 60 degrees negative, the accuracy of the dew point meter is guaranteed to be within plus or minus 2 degrees. When the accuracy is slightly lower, the dew point meter can reach a dew point of -80 degrees.
There are three methods commonly used to measure dew point today: The working principle of SHAW dew point meter and the use of SADP dew point meter
The first, with 60 years of practical experience in the field of moisture measurement, the sensor developed by the Shore Dewometer using polymer film specifically for measuring low dew point is stable, free from condensed water, most chemicals, and The dew point meter used adopts zero-point automatic calibration, and the two patented technologies of gain return make the dew point measurement range wide, high precision, long-term stability and excellent cost performance.
The second, cold mirror method, metal oxide method and polymer method. The cold mirror method achieves high accuracy over a wide measurement range, but due to the limitations of its optical measurement principle, it is highly susceptible to specular contaminants and dust, which affects accuracy and makes it difficult to distinguish between frost and dew point. In order to overcome the above shortcomings, the measuring system often adds many additional functions such as mirror cleaning and protection, which makes the whole set of equipment more expensive. This measuring method is often used for high precision and good operation and maintenance conditions, such as laboratory. Maintenance costs are high for most online measurements.
Third, metal oxide sensors, including sensors for low dew point measurement in industrial process control, can measure very low dew points when used correctly. The disadvantage is poor long-term stability, which is caused by drift caused by the humidity sensor itself. The calibration work is indispensable, the sensor can not be calibrated online, in most cases it should be sent to the original factory calibration and the calibration cost is high, which will affect the accurate measurement, normal production, increase maintenance, workload, and metal oxidation in the future. Once the sensor is damaged in high humidity or condensation, its function will not recover. Introduction to the working principle of SHAW dew point meter and the use of SADP dew point meter
The temperature and humidity sensor consists of two parts: a capacitive polymer film moisture sensor and a resistance type temperature sensor. The humidity sensor measures water molecules in the gas to be measured to measure relative humidity. The temperature sensor measures the surface of the moisture sensor. Humidity, the built-in microprocessor of the instrument calculates the dew point from these two parameters. The humidity measuring and temperature measuring sensors are closely close to each other through the metal film, so that the temperature measuring sensor can accurately measure the temperature of the humidity sensor on the one hand, and the induction capacitance generated by the external electric field is greatly reduced by the action of the metal film on the other hand. Therefore, the measurement accuracy is improved. In the case of low humidity, the reaction time of the sensor is 40-240 seconds, depending on the direction and magnitude of the humidity change, and the reaction time is high when measuring high humidity. The temperature range is -40-+180 degrees, and the pressure range is 0-20 bar. Its corrosion resistance is also outstanding. It has good adaptability to alkaline and weak acid gases, usually in the case of low humidity. The film moisture sensor should have a minimum dew point of -9 degrees with a dew point accuracy of +2 degrees. It can be measured with the British Shore SHAW sensor and automatic calibration patent technology while ensuring +2 degree dew point temperature accuracy. The minimum dew point is -60 degrees, and a dew point of -80 degrees can be achieved with a slightly lower accuracy because the self-calibration technique makes accurate relative humidity measurements possible. During the self-calibration process, the temperature measuring resistor cools the Shore dew point probe to a temperature 10 degrees above ambient temperature, and the instrument measures the real-time temperature and relative humidity during the cooling process. From the formula RH=RH0+PW/PWS (where RH is the measured value of the instrument. RH0 is the intercept of the straight line on the Y-axis. PW is the partial pressure of water and gas in the gas to be measured at this moment, assuming a certain value. PWS is the saturated water pressure Value.1/PWS is a function of temperature. It can be seen that the RH and 1/PWS values ​​of several sets of different temperatures can be used to derive a fitted straight line, and the intercept RH of the fitted straight line on the Y-axis is derived. When high, the measured relative temperature of the sensor is offset by the value of the zero point.

Introduction to the working principle of SHAW dew point meter and the use of SADP dew point meter

After determining RH0, accurate RH calculation can be performed to accurately calculate the dew point. When the relative humidity is lower than 10%, the system automatically performs the self-calibration function. At this time, the last output parameter is locked, and the system can be output after calibration. Measurements. The self-calibration function can also be started in time intervals (usually 6 hours). If the temperature or dew point measurement is unstable during the calibration process, ie the environmental impact cooling process or the assumed PW is a constant condition, the self-calibration function will be executed again after the set time interval, and so on, until the temperature The true dew point is output after the dew point temperature is stable. Accurate measurement of low moisture dew points is achieved through the excellent Shore dew point hardware design and automatic calibration software. The long-term accumulation of certain chemical gas molecules inside the humidity sensor affects the measurement accuracy. In order to ensure accurate measurement, the gain regression software was developed. The working process is to perform the gain regression function before the zero-point automatic calibration software is executed. The Shore dew point sensor is heated to 160 degrees to evaporate the chemical gas molecules accumulated inside it. Accurate measurement. At the same time, this method eliminates the problem that oil accumulation affects the reaction time. Xiao's dew point meter moisture sensitive device is not afraid of condensed water. Natural air drying after condensation does not affect normal use, but the instrument needs to be taken out when air drying, which will affect the normal operation of other work. In order to prevent such frequent occurrences, The dew point meter also has a protection function, that is, when the humidity unexpectedly rises to 80% RH, the temperature sensor immediately heats the humidity sensitive device to reduce the local relative humidity to avoid the formation of saturated water vapor. By using this customer-friendly feature, the downtime is greatly reduced, which increases productivity. The dew point meter is factory set to -80+20 degrees dew point corresponding to 4~20MA, but the customer can modify the parameters within any range by software modification, such as: -60~~+5 degree dew point or -75~~+15 degree, etc. 4 -20MA output, which greatly facilitates the subsequent cascade control. All dew point meters will drift after using for a period of time. Most dew point meter customers can't make their own corrections. They can only be sent to the factory frequently to spend a certain amount of money and time for correction. For the convenience of customers, the dew point meter can make customers In the case that you can find the standard humidity, the utility software can make corrections by itself, which greatly saves the cost and time and ensures the normal measurement. Through the use of a number of cutting-edge technologies.

For more information on the working principle of the SHAW dew point meter and the use of the SADP dew point meter , please call the British Xiao Instrument 021-66015906 or visit

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