The temperature sensor selection should pay attention to the point
(1) choose measurement range
and measurement of weight, temperature, choose the humidity sensor to determine the measurement range in the first place. In addition to weather, outside the department, temperature and humidity measurement and control of generally don't need the wet process ( 0 ~ 100% rh) Measurement.
2. Choose measurement accuracy
measurement accuracy is the most important indicator of humidity sensor, per - Percentage for humidity sensor is a higher level, or even better. Because to achieve different precision, the manufacturing costs vary widely, the price also differs very far. So the user must act according to actual circumstances, should not blindly pursue 'high, refined, sharp'. As at different temperatures using a humidity sensor, and its value to consider the influence of temperature drift. As is known to all, is a function of temperature, relative humidity temperature greatly affects the relative humidity within a specified space. 01 ℃ temperature of each change. Will result in a change to the humidity of 05% RH ( Error) 。 Use occasions if difficult to achieve constant temperature, high humidity measurement accuracy is not appropriate. In most cases, if there is no precise temperature control means, or measured space is sealed, the precision of + / - 5% RH is enough. Accurate control for the local space of constant temperature, constant humidity, or need to track humidity change Settings at any time, to choose more than + / - 3% RH precision humidity sensor. And the accuracy is higher than the requirements of + / - 2% RH even sensor calibration standard humidity generator also hard to do, what's more, the sensor itself. Relative humidity measuring instrument, even at 20 ℃ - Under 25 ℃, 2% RH accuracy is still very difficult. Usually feature is given in the product information in the normal temperature ( 20℃±10℃) And clean gas measurement.
3. Consider the drift and temperature drift
in be used actually, because of the influence of the dust, oil pollution and harmful gas, use a long time, electronic moisture transfer device can produce aging, precision, electronic moisture transfer in drift amount is general in the plus or minus 2%, even higher. In general, the effective use of production vendors will indicate one calibration time is 1 year or 2 years, due to calibration.
(4), and other considerations for
humidity sensor is sealing, to protect the measuring accuracy and stability, and should be avoided in acid, alkali and containing organic solvents used in the atmosphere. Also avoid using dust in the larger environment. For the correct reflection to measure the humidity of the space, also should avoid sensors placed too close to the walls or the flow of air is not blind Angle. If the room is too large to be measured, it should be placed more sensors. Some humidity sensor to power supply requirement is higher, otherwise will affect the accuracy of measurement. Or mutual interference between sensors, even unable to work. When using, should according to the technical requirements to provide appropriate, conform to the requirements of the precision of power supply. Sensor need for remote signal transmission, to pay attention to the attenuation of the signal problem. When the transmission distance of more than 200 m or more, the proposal chooses humidity sensor output signal frequency.
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key words: thermal resistance, thermocouple, thermal resistance, platinum resistance, PT100, PT1000, pressure sensor and digital temperature sensor