Temperature and humidity sensor (Part 4)
- Mar 23, 2018 -
Matters needing attention
Select the matters needing attention of 
1) choose measurement range
And selection measure weight, temperature, humidity sensor must first determine the measurement range.In addition to weather, outside the department, temperature and humidity measurement and control of general don't need the wet process (0-100% RH) measurement.
(2) choose measurement precision
Accuracy of measurement is the most important indicator of humidity sensor, every increase - percentage points, for the 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.Every 0.1 ℃ temperature changed.Will result in a change to the humidity of 0.5% 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 to 25 ℃, to achieve the accuracy of 2% RH is still very difficult.Usually feature is given in the product information at room temperature (20 ℃ + 10 ℃) and clean gas measurement.
(3) considering 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 humidity sensor in scatter is generally 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) other considerations
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.
Folding edit this paragraph industry demand
The food industry: the temperature and humidity is critical for food storage, temperature and humidity changes can cause food spoilage, cause food safety problems of temperature and humidity monitoring is conducive to timely control the related staff.
File management: paper products is extremely sensitive to temperature and humidity, improper save can seriously reduce the file save fixed number of year, with the temperature and humidity on the transmitter with fan, dehumidifier, heater, can keep a stable temperature, avoid pests, wet, etc.
Greenhouses: plants for temperature and humidity requirement is very strict, improper temperature and humidity, the plants will stop growing and even death using temperature and humidity sensor, gas sensor, light sensor, and can be composed of a greenhouse digital temperature and humidity monitoring and control system, control the related parameters inside the agricultural greenhouses, which shed efficiency to achieve perfection.
Animal breeding: all kinds of animals under different temperature will show different growth condition, the goal of high quality high yield depends on appropriate environment to guarantee.
Drug storage: according to the relevant national requirements, drug preservation should be carried out in accordance with the appropriate temperature and humidity control.According to the latest GMP certification, for general drug storage temperature range of 0 to 30 ℃.
Tobacco: tobacco raw material in the fermentation process to control the temperature and humidity, under the condition of the site environment and convenient to use wireless temperature and humidity, temperature and humidity monitoring in complex environment of the scene, can use RS - 485 control temperature and humidity sensor for testing digital transmission, such as the temperature and humidity of the cigarette package, avoid pests, if improper operation, can cause loss of hundreds of raw materials.
Industrial control industry: mainly used in hvac, machine room monitoring, etc.Building the environmental control temperature control, usually with humidity control to achieve best attention increasingly comfortable environment.