SHT20 Industrial Temperature & Humidity Sensor
User Manual

Model: YTL-SHT20-RS485 | Chip: SHT20 (Sensirion, Switzerland) | RS485 MODBUS RTU | Power Supply: 9~18 VDC

1. Product Overview

This sensor uses the high-precision digital temperature and humidity chip SHT20 from Sensirion, Switzerland, combined with an industrial RS485 interface and MODBUS RTU protocol. It is suitable for building automation, HVAC, warehouse monitoring, agricultural greenhouses, server room monitoring, and other applications.

2. Technical Specifications

Parameter	Specification
Supply Voltage	9~18 VDC (12V or 24V power adapter recommended)
Power Consumption	≤0.2W (approx. 15mA @ 12V)
Temperature Measurement Range	-40℃ ~ +125℃
Temperature Accuracy	±0.3℃ (typical @ 25℃)
Humidity Measurement Range	0~100% RH (non-condensing)
Humidity Accuracy	±3% RH (typical @ 25℃, 20~80%RH)
Communication Interface	RS485 (half-duplex)
Communication Protocol	MODBUS RTU
Baud Rate	9600 (default, configurable 4800/19200/38400)
Data Format	8 data bits, no parity, 1 stop bit (8N1)
Device Address	1~247 (default 1, configurable)
Response Time	≤ 2s (data refresh)
Operating Environment	-40℃ ~ +85℃, 0~99%RH (non-condensing)
Enclosure Protection	Plastic/Aluminum alloy optional, IP65 (confirm when ordering)
Dimensions	Approx. 90×45×30mm (excluding probe)

3. Wiring Instructions

Terminal Label	Description	Wiring Recommendation
VCC	Power Positive (9~18V DC)	Connect to 12V or 24V power positive
GND	Power Negative	Connect to power negative, also serves as RS485 reference ground
A / 485A	RS485 A+ (non-inverting)	Connect to host (PLC/DAQ) A+
B / 485B	RS485 B- (inverting)	Connect to host B-

📌 Note: Shielded twisted-pair cable is recommended, with A+ and B- as a twisted pair. For long-distance communication (>100m), 120Ω termination resistors should be connected at both ends of the bus.

4. MODBUS Communication Protocol

4.1 Register List (Function Code 03 / 04)

Register Address (HEX)	Parameter	Data Type	Description
0x0000	Temperature	16-bit signed integer	Unit: 0.1℃, actual value = register value ÷ 10 Example: 0x012E = 302 → 30.2℃
0x0001	Humidity	16-bit unsigned integer	Unit: 0.1%RH, actual value = register value ÷ 10 Example: 0x0320 = 800 → 80.0%RH
0x0100	Device Address	16-bit	1~247, default 1, supports function code 06
0x0101	Baud Rate	16-bit	0:9600, 1:4800, 2:19200, 3:38400, default 0

Note: Power cycle is required after modifying address/baud rate for changes to take effect.

4.2 Read Temperature and Humidity Example

        Host Request (Address 1):

        01 04 00 00 00 02 71 CB

        Slave Response (Temperature 25.6℃, Humidity 53.2%):

        01 04 04 01 00 02 14 7A 69

        Parsing: Temperature: 0x0100 = 256 → 25.6℃; Humidity: 0x0214 = 532 → 53.2%RH

4.3 Modify Device Address Example

        Change address 1 to address 2 (function code 06, address 0x0100):

        01 06 01 00 00 02 89 F6

        (Returns same message on success)

5. Usage Steps

Wiring: Connect power and RS485 lines according to terminal definitions.
Power On: The sensor indicator light (if available) will flash once.
Communication Test: Use a MODBUS master (e.g., PC serial tool, PLC, DTU) to send read commands.
Data Parsing: Calculate actual temperature/humidity according to register definitions.
Parameter Modification (optional): Send write register commands to modify address or baud rate.

6. Important Notes

⚠️ Important Notes:
1️⃣ Avoid long-term exposure of the sensor to condensing environments, which may affect accuracy and chip lifespan.
2️⃣ RS485 communication lines should be routed separately from power cables.
3️⃣ If multiple sensors are connected on the same bus, addresses must be unique.
4️⃣ Use a regulated power supply. Do not exceed 18V DC.
5️⃣ The housing is not waterproof. For outdoor use, a protective cover is required (waterproof type optional).

7. Troubleshooting

Phenomenon	Possible Cause	Solution
No data returned	Wiring error, address/baud rate mismatch	Check A/B wiring, verify host parameters
Data is 0 or unchanged	Communication interference, sensor damaged	Add termination resistors, check power supply
Abnormal temperature jumps	Uncalibrated or affected by heat source	Keep away from heat sources, restore factory settings
Humidity stuck at 100%	Sensor condensation or aging	Dry treatment, or replace sensor

8. Package Contents

Temperature & Humidity Sensor Body ×1
Terminal block / Waterproof connector ×1
Certificate of Conformity ×1
(Optional) RS485 to USB debugging cable

9. Technical Support

For more detailed MODBUS register tables, CRC check routines, or custom protocols, please contact the manufacturer.

SHT20 Industrial Temperature & Humidity SensorUser Manual