Step 1: Identify the Measurement Parameter and Application

S+S REGELTECHNIK organizes its products into six parameter-based families, each under a registered trademark. Start by confirming what you need to measure:

Step 2: Determine the Installation Type (Temperature Sensors)

S+S offers the industry's most comprehensive range of installation options for temperature sensors (THERMASGARD®). Match your scenario below:

Step 3: Choose the Sensing Element

The sensing element is one of the most critical decisions in sensor selection, directly affecting accuracy, linearity, temperature range, and cost. S+S offers the following mainstream options:

3.1 Platinum RTD (Pt100 / Pt1000)

• Characteristics: Excellent linearity, highest accuracy, best long-term stability, strong interchangeability
• Accuracy Classes: Class A (±0.15°C @ 0°C), Class AA (±0.10°C @ 0°C), 1/3 DIN (±0.10°C @ 0°C), 1/10 DIN (±0.03°C @ 0°C)
• Pt100 vs Pt1000: Pt100 (100Ω @ 0°C) suits short connections; Pt1000 (1000Ω @ 0°C) minimizes lead wire resistance effects — preferred for distances over 10m
• Best for: Laboratories, pharmaceuticals, cleanrooms — applications demanding the highest accuracy
• Cost: Higher

3.2 Nickel RTD (Ni1000 / NiTK)

• Characteristics: Higher sensitivity than platinum (larger temperature coefficient), but narrower temperature range
• Best for: Standard HVAC applications, indoor temperature monitoring
• Cost: Medium

3.3 NTC Thermistors (NTC1.8K / NTC10K / NTC20K)

• Characteristics: Highest sensitivity (large resistance change), but non-linear — requires linearization
• Best for: DDC controller integration — most common in building automation systems
• Cost: Lower
• Note: Different DDC brands use different NTC curves; S+S offers special curve versions like NTC10K (B=3695K)

3.4 Silicon Temperature Sensors (KTY81-210 / LM235Z)

• Characteristics: Good linearity, compact, direct voltage output
• Best for: Embedded systems, simple temperature control
• Cost: Low

Step 4: Output Signal and Communication Protocol

S+S sensors offer a rich variety of output options. Choose based on your control system interface:

4.1 Passive Output

The sensor directly outputs a resistance value (e.g., Pt100 outputs 100Ω @ 0°C) or voltage (e.g., LM235Z), requiring an external transmitter or direct DDC reading. Simple and low-cost, but not suitable for long-distance transmission — lead wire resistance affects accuracy.

4.2 Active Analog Output

• 0-10V: Most common, transmission up to 100m, good noise immunity, compatible with most BMS platforms
• 4-20mA: Long distance (500m+), strongest noise immunity, broken-wire detection (0mA = fault) — preferred for industrial environments
• 0-5V / 1-6V: Specific system compatibility requirements

4.3 Digital Communication Protocols

• Modbus RTU (RS-485): The most universal industrial digital protocol, supports multi-drop bus topology with up to 32 devices per bus
• BACnet MS/TP: Purpose-built for building automation, native compatibility with Siemens Desigo, Honeywell, and other BMS platforms
• EtherCAT: Industrial Ethernet protocol for high-speed real-time control; S+S offers EtherCAT P (with power) versions
• Bluetooth: Select models support Bluetooth configuration and readout for convenient field commissioning

5. Humidity Sensor Selection Notes

S+S HYGRASGARD® humidity sensor selection is more straightforward than temperature, but key decisions remain:

• Measurement Parameter: Relative humidity only (RH%), combined temperature/humidity (RH+T), or full version with dew point/enthalpy calculation. If you need temperature data too, the combined model is more cost-effective and simpler to install.
• Installation Type: Indoor (wall), duct (insertion), outdoor (radiation shield) — same logic as temperature sensors.
• Output Signal: 0-10V or 4-20mA analog, or Modbus/BACnet digital.
• Display Option: Select models available with LCD display and operating buttons (SD version) for convenient field viewing and configuration.

6. Pressure Sensor Selection Notes

For PRESSGARD® series, confirm the following:

• Pressure Type: Differential pressure is the most common type, used for cleanroom pressure monitoring and filter status detection. Gauge pressure and absolute pressure serve specific industrial scenarios.
• Range: Common ranges include ±100Pa, 0-500Pa, 0-1000Pa. Always select a range slightly above your actual requirement to protect the sensor.
• Overload Capacity: S+S pressure sensors feature good overload protection, but confirm the one-way and two-way overload limits match your operating conditions.

7. Real-World Selection Examples

Example 1: Office Building HVAC Room Temperature

Example 2: Pharmaceutical Cleanroom T&RH Monitoring

Example 3: Ventilation Duct Temperature

8. Understanding S+S Order Codes

S+S REGELTECHNIK uses a fixed-format order code. Understanding its structure helps quickly confirm product configuration. Example for RTF1 Pt100:

Order No.: 1101-40A0-1003-000

• 1101: Product series prefix
• 40: Product type code (40 series = indoor type)
• A0: Version/option code
• 1003: Sensing element code (1003 = Pt100)
• 000: Special option code (000 = standard configuration)

Coding conventions vary slightly across product families. Please refer to official datasheets or contact the Ruilianxin technical team to confirm complete order codes.

9. Common Selection Mistakes to Avoid

• Mistake 1: Higher accuracy is always better. In reality, choose the accuracy class that matches your application. Standard HVAC can use NTC; only labs and pharma need Pt100 Class A or above.
• Mistake 2: Ignoring the impact of installation location on readings. Indoor sensors installed on exterior walls, near heat sources, in direct sunlight, or near vents will produce biased readings. Always follow installation best practices.
• Mistake 3: Confusing Pt100 and Pt1000. While accuracy is identical, Pt1000 suffers less from lead wire resistance in long runs. If the sensor-to-panel distance exceeds 10m, prefer Pt1000.
• Mistake 4: Overlooking IP rating. Outdoor and duct installation scenarios require IP65 protection. Standard indoor models (IP30) cannot be used outdoors.
• Mistake 5: Not checking the pressure sensor range. A sensor with too small a range may trigger overload protection under normal conditions. Choose a range at least 1.5× the maximum expected operating pressure.