Resistance Temperature Detectors (RTDs)

 Resistance Temperature Detectors (RTDs) like Pt100 and Pt1000 are platinum-based sensors widely used for precise temperature measurement due to their linear resistance-temperature relationship, stability, and accuracy. The "Pt" stands for platinum, and the numbers (100 or 1000) indicate the nominal resistance at 0°C (100 ohms for Pt100, 1000 ohms for Pt1000). Below is an overview of Pt100, Pt1000, and other related RTD models, their characteristics, and common configurations.

Common RTD Models

1. Pt100:
   • Nominal Resistance: 100 ohms at 0°C.
   • Temperature Range: Typically -200°C to +650°C, though some designs extend to +850°C with specific insulation or sheathing.
   • Accuracy: High accuracy (±0.1°C to ±0.3°C, depending on class, e.g., Class A, B, 1/3 DIN).
   • Sensitivity: ~0.385 ohms/°C (based on IEC 60751 standard with α = 0.00385 Ω/Ω/°C).
   • Construction:
     • Wire-Wound: Platinum wire coiled around a ceramic or glass core, ideal for high accuracy and wide temperature ranges.
     • Thin-Film: Platinum layer deposited on a ceramic substrate, more cost-effective, faster response, but slightly less robust for extreme conditions.
   • Applications: Common in process industries (e.g., chemical plants, oil refineries) due to compatibility with a wide range of instruments.
2. Pt1000:
   • Nominal Resistance: 1000 ohms at 0°C.
   • Temperature Range: Typically -50°C to +500°C, though some designs reach -200°C to +600°C.
   • Accuracy: Similar to Pt100 but with higher sensitivity (~3.85 ohms/°C), reducing errors from lead wire resistance, especially in 2-wire setups.
   • Sensitivity: ~10x higher than Pt100, making it more suitable for applications requiring high resolution.
   • Construction: Primarily thin-film due to higher resistance, though wire-wound versions exist for specialized applications.
   • Applications: Preferred in battery-powered systems (less power consumption, less self-heating) and applications like HVAC, refrigeration, automotive, and 3D printing.
3. Other Platinum RTD Models:
• Pt50: 50 ohms at 0°C, less common, used in specialized applications.
• Pt200: 200 ohms at 0°C, rare, used for specific industrial needs.
• Pt500: 500 ohms at 0°C, less common, balances sensitivity and compatibility.
• Pt2000: 2000 ohms at 0°C, very rare, used in niche high-sensitivity applications.
• Temperature Range: Varies by model, typically -200°C to +850°C, depending on construction and tolerance.
• Applications: These are less common but used in specific laboratory or industrial settings requiring unique resistance characteristics.
5. Non-Platinum RTDs:
   • Ni100/Ni120: Nickel-based, 100 or 120 ohms at 0°C, narrower range (~-60°C to +300°C), more susceptible to corrosion.
   • Cu10: Copper-based, 10 ohms at 0°C, highly linear but limited to ~150°C due to oxidation.
   • Ni-Fe 604: Nickel-iron, 604 ohms, used in specific industrial applications.
   • Applications: Used in cost-sensitive or specialized applications where platinum’s cost or range isn’t justified.

Key Differences Between Pt100 and Pt1000

Feature	Pt100	Pt1000
Nominal Resistance	100 ohms at 0°C	1000 ohms at 0°C
Sensitivity	~0.385 ohms/°C	~3.85 ohms/°C
Accuracy	High (±0.1°C to ±0.3°C, Class A/B)	Similar, but higher resolution
Lead Wire Error	More sensitive to lead resistance (~0.4 K/m in 2-wire)	Less sensitive (~0.04 K/m in 2-wire)
Power Consumption	Higher (requires more current)	Lower (ideal for battery-powered systems)
Self-Heating	Lower for same current, but higher overall	Higher, but can be mitigated with low current (<0.1 mA)
Construction	Wire-wound or thin-film	Mostly thin-film, some wire-wound
Applications	Process industries, labs	HVAC, refrigeration, automotive, 3D printing
Compatibility	Wider instrument compatibility	May require specific electronics

Configurations and Wiring

• 2-Wire: Simplest, but lead wire resistance introduces significant errors, especially for Pt100 (~0.4 K/m). Suitable for Pt1000 with short cables (<5 m)
• 3-Wire: Compensates for lead wire resistance, common in industrial applications for both Pt100 and Pt1000.
• 4-Wire: Most accurate, eliminates lead wire resistance entirely, ideal for high-precision applications.
• Connectors: Probes may include thermowells, threaded fittings (e.g., 1/2" NPT), or cable probes for flexibility.

Tolerance Classes (IEC 60751)

• Class AA: ±(0.1 + 0.0017|t|)°C, highest precision.
• Class A: ±(0.15 + 0.002|t|)°C, common for industrial use.
• Class B: ±(0.3 + 0.005|t|)°C, standard for general applications.
• 1/3 DIN, 1/10 DIN: Tighter tolerances for specialized applications, reducing uncertainty.

Specific Models and Examples

• Pt100 Models:
  • Omega EM500-PT100: Straight tube, armored, or threaded probes, -200°C to +800°C, customizable for industrial use.
  • ItalCoppie TRECOSTP: -50°C to +500°C, 2/3/4-wire, Class AA/A/B.
  • Japsin Instrumentation PT-100: 3-wire, PTFE-coated, -50°C to +400°C, with head assembly.
• Pt1000 Models:
  • Slice Engineering Pt1000/Pt100: Designed for 3D printing, -50°C to +500°C, 2-meter bare leads, compatible with MAX31865 amplifier for Pt100.
  • ItalCoppie TRMSTD: -50°C to +500°C, 2/3/4-wire, Class AA/A/B, minimum 3 mm diameter.
  • Carremm Controls PT1000: 2" to 11.5" probes, 1/4" diameter, 500°F max, customizable leads and fittings.

Applications

• Pt100: Industrial processes, laboratories, food processing, and chemical plants due to wide compatibility and robustness.
• Pt1000: Battery-powered devices, HVAC, refrigeration, automotive, and 3D printing due to lower power consumption and higher sensitivity.
• Other Models: Niche applications in research, biomedical, or cost-sensitive environments (e.g., Ni100 for HVAC, Cu10 for low-temperature systems)

Calibration and Testing

• Calibration: Use controlled temperature sources (e.g., ice bath at 0°C, boiling water at 100°C, or dry block calibrators) and compare against a resistance-temperature chart (e.g., Pt1000 at 126°C = 1483.30 ohms).
• Testing: Measure resistance with a precision multimeter and verify against expected values to detect drift, hysteresis, or damage.

Considerations for Selection

• Pt100: Choose for industrial systems requiring compatibility, wider temperature ranges, or where 3/4-wire setups are standard.
• Pt1000: Opt for applications with long cable runs, battery-powered systems, or where higher resolution is needed.
• Other Models: Select based on specific needs (e.g., cost, temperature range, or material compatibility).