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Shanghai Hujing Medical Equipment Co., Ltd
Working principle of temperature, humidity and pressure difference tester
Date: 2025-07-08Read: 4
The temperature, humidity, and pressure difference tester is an integrated portable instrument mainly used to simultaneously monitor and record the temperature, humidity, and pressure difference (pressure difference) between spaces in the environment. The core working principle is to combine three different sensor technologies with signal processing systems, as follows:
1、 Temperature measurement principle
Sensor type: Thermistors (such as PT100/PT1000 platinum resistors) or thermocouples are usually used.
Working principle:
Thermistor: The characteristic that the resistance value of a conductor or semiconductor changes with temperature. When the temperature rises, the resistance value undergoes a predictable change (positive or negative temperature coefficient). The internal circuit of the instrument measures this resistance value and accurately calculates the corresponding temperature value through a calibration formula.
Thermocouple: Utilizing the temperature difference between two different metal connection points (thermocouple junction) to generate a small voltage (Seebeck effect). The instrument measures this voltage and references the cold end compensation temperature to calculate the actual temperature of the hot end.
2、 Principle of humidity measurement
Sensor type: The most commonly used is capacitive humidity sensor.
Working principle:
The sensor core is a polymer film or specially treated ceramic substrate that is sensitive to water molecules, with electrodes covering both sides to form a capacitor.
When water vapor in the environment is absorbed or desorbed by this moisture sensitive material, the dielectric constant of the material will change accordingly.
The change in dielectric constant directly leads to a change in capacitance value.
The internal circuit of the instrument accurately measures the change in this small capacitance and converts it into the corresponding relative humidity (% RH) reading. Sensors typically require temperature compensation to obtain more accurate results.
3、 Principle of Differential Pressure Measurement
Sensor type: The core is a differential pressure sensor.
Working principle:
There is a very thin silicon film (or metal film) inside the sensor.
The two sides of the membrane are connected to the two spaces where pressure difference needs to be measured (such as room and corridor, clean room and buffer room) through the high pressure end (+) interface and low pressure end (-) interface on the instrument.
When the air pressure of two spaces acts on both sides of the diaphragm, a pressure difference (Δ P) will be generated.
This pressure difference causes extremely small physical deformation (bending) of the diaphragm.
The pressure resistance element (strain gauge) or capacitor plate integrated on the membrane will detect this deformation:
Piezoresistive type: Deformation causes a change in the resistance value of the piezoresistive element, forming a Wheatstone bridge output signal.
Capacitive: Deformation causes a change in the capacitance value between the membrane and the fixed electrodes on both sides.
Sensors convert this physical deformation into an electrical signal proportional to the pressure difference (usually voltage or current).
The electronic circuit inside the instrument accurately amplifies and processes this weak electrical signal, and converts it into a differential pressure display (in units such as Pa, inH2O, mmH2O, etc.).
4、 Overall workflow
1. Data collection: Temperature sensors and humidity sensors respectively obtain physical quantities (heat, water vapor) in the environment, while differential pressure sensors connect two spaces through hoses to obtain physical deformation caused by pressure differences.
2. Signal conversion: All sensors convert the sensed physical quantities into weak electrical signals (resistance, capacitance, voltage/current changes).
3. Signal conditioning: The high-precision circuit (amplifier, analog-to-digital converter ADC) inside the instrument amplifies, filters, and converts these weak signals into digital signals.
4. Data processing and compensation: The built-in microprocessor (MCU) receives digital signals:
Apply pre stored sensor calibration parameters and algorithms for calculation.
Perform necessary compensation operations (such as temperature compensation for humidity sensors, linear compensation for pressure sensors, and temperature compensation).
Calculate accurate temperature values, relative humidity values, and pressure differentials.
5. Display and output: The calculation results are displayed in real-time on the instrument screen (usually LCD or OLED). Instruments usually also have data recording (storage), alarm functions (over limit prompt), and the ability to transmit data to computers or mobile phones for further analysis through USB/Bluetooth and other means.
5、 Core application value
This three in one instrument is particularly suitable for places that require strict control of environmental parameters:
1. Cleanroom (pharmaceutical, electronic, biological laboratory): Monitor the pressure gradient of the room to ensure cleanliness (positive pressure prevents external contamination from entering, negative pressure prevents hazardous substances from leaking), while monitoring whether the temperature and humidity meet the process requirements.
2. HVAC system debugging and maintenance: check the air duct pressure difference, filter resistance, room pressure balance, and environmental comfort (temperature and humidity).
3. Medical facilities (operating rooms, isolation wards): Maintain necessary pressure differentials to control infections and ensure appropriate temperature and humidity.
4. Building enclosure structure testing: measuring the pressure difference inside and outside the building.
5. Laboratories, data centers, and other places that require precise environmental parameters.
In summary, the temperature, humidity, and pressure difference tester senses the temperature, humidity, and pressure difference of the environment through three different types of sensors. It uses electronic technology to convert these physical signals into electrical signals, which are then precisely calculated, compensated, and calibrated. Finally, it outputs three key environmental parameter values in digital form, providing an efficient and convenient tool for environmental monitoring and management.