Identity

The DHT22 Sensor is an environmental microclimate telemetry module containing a polymer capacitive humidity sensor and an NTC thermistor, utilized to transmit digital temperature and humidity data to facility controllers.

Overview

The DHT22 Sensor is a high-priority, low-cost environmental sensor that processes analog signals into a digital single-bus protocol. It is vital for providing continuous temperature and humidity readings to the Smart Controller. It is prone to saturation, sensor drift from corrosive ammonia, and dust buildup within the poultry environment, necessitating regular calibration or bake-out cycles to prevent operational failures.

Structured Facts

Classification

Environmental Microclimate Telemetry Equipment / Automated.

Purpose

Monitors ambient temperature and relative humidity inside automated livestock facilities to feed digital telemetry to environmental controllers.

Working Principle

Combines a polymer capacitive relative humidity sensing element and an NTC thermistor. The polymer film absorbs water vapor, altering its dielectric constant and capacitance. The NTC thermistor's metal oxide semiconductor changes electrical resistance with temperature. An on-board 8-bit microcontroller processes these analog signals, applies OTP memory calibration coefficients, and outputs a digital signal via a proprietary single-bus, timed-pulse serial protocol over a single data wire.

Technical Specifications

• Signal Output Resolution: 16-bit (0.1°C and 0.1% RH).
• Physical Sampling Rate: 0.5 to 1.0 Hz (Once every 1 to 2 seconds).
• Sensing Module Weight: 2.4 g.
• Max Shielded Cable Length: 20 m.

Capacity

• Temperature Measuring Range: -40°C to +80°C (Maximum Limit: 125°C).
• Relative Humidity Range: 0% to 100% RH.

Installation Requirements

Must be installed away from draft zones, heaters, and direct light. Requires a 4.7kΩ to 10kΩ pull-up resistor on the data line to prevent communication errors. A 100 nF decoupling capacitor should be placed between VDD and GND to filter power noise. Connects to digital input pins of the Smart Controller.

Operating Parameters

• Operational Supply Voltage: 3.3 to 6.0 VDC (Typical: 5.0 VDC).
• Measurement Current Draw: 1.0 to 1.5 mA (Maximum Peak: 2.5 mA).
• Standby Current Draw: 40 to 50 µA.

Maintenance

If saturated, requires a recovery bake-out cycle: dry-heat at 50°C to 60°C with <10% RH for 2 hours, then rehydrate at 20°C to 30°C with >70% RH for 5 hours.

Cleaning & Disinfection

Not waterproof. Do not expose to direct water sprays or heavy condensation.

Advantages

Low-cost, reliable, provides digital single-bus telemetry directly to the controller.

Limitations

Not waterproof; fails if exposed to water or heavy condensation. Corrosive gases like ammonia (NH3) and dust coat the polymer substrate, causing sensor drift and slower response times. Omission of the pull-up resistor causes packet loss.

Safety Precautions

Keep away from water sprays and corrosive disinfection chemicals.

Quantitative Data

• Dimensions: Max Shielded Cable Length 20 m.
• Weight: 2.4 g.
• Power Requirement: Measurement Current Draw 1.0 to 1.5 mA; Standby 40 to 50 µA.
• Voltage: 3.3 to 6.0 VDC (Typical: 5.0 VDC).
• Operating Temperature: Measuring Range -40°C to +80°C (Max 125°C).
• Accuracy: Temperature Measurement Accuracy +/- 0.5°C; Humidity Measurement Accuracy +/- 2% RH (Max Error: +/- 5% RH).

Relationships

• Housing Systems: All automated environment facilities.
• Environmental Controls: Smart Controller.
• Production Stages: All stages.
• Related Equipment: Smart Controller, Automated Ventilation Systems.
• Maintenance SOPs: Recovery bake-out cycle.