Short answer
A Pt100 element produces exactly 100.00 Ω at 0 °C, increasing by approximately 0.385 Ω for every 1 °C temperature rise. A Pt1000 element produces 1,000.0 Ω at 0 °C, providing ten times the electrical sensitivity (3.85 Ω/°C). That tenfold increase fundamentally alters how vulnerable the measurement loop is to field wiring resistance, terminal oxidation, and barrier drops.
Quick reference: Pt100 vs. Pt1000 Platinum RTD Field Engineering Comparison (IEC 60751)
| Parameter | Pt100 Platinum RTD | Pt1000 Platinum RTD |
|---|---|---|
| Nominal Resistance at 0 °C | 100.00 Ω | 1,000.0 Ω |
| Sensitivity (Slope) | 0.385 Ω / °C | 3.85 Ω / °C (10× higher) |
| Temperature Coefficient (α) | 0.00385 Ω/Ω/°C | 0.00385 Ω/Ω/°C |
| Lead Wire Resistance Error (2-wire) | 2.6 °C error per 1.0 Ω wire resistance | 0.26 °C error per 1.0 Ω wire resistance |
| Recommended Wiring Topology | 3-wire or 4-wire (mandatory for runs >5 m) | 2-wire usable for HVAC; 3-wire for precision |
| Typical Excitation Current | 1.0 mA (dissipates 0.1 mW) | 0.1 mA to 0.2 mA (prevents self-heating) |
| Typical Industrial Applications | Petrochemical, refining, power generation | HVAC, cleanrooms, solar thermal, battery energy |
What to look for
In a 2-wire installation, every 1.0 Ω of copper lead resistance adds an artificial +2.6 °C offset error to a Pt100 reading, but only +0.26 °C to a Pt1000 reading. For runs extending past 15 meters, Pt100 installations strictly require a 3-wire or 4-wire configuration to cancel lead resistance, whereas Pt1000 sensors can often operate with acceptable accuracy over simple 2-wire circuits in HVAC or non-critical monitoring.
Excitation current is another critical design boundary. Analog input cards typically supply 1.0 mA of constant excitation current through a Pt100 element (dissipating 0.1 mW). Pumping that same 1.0 mA through a Pt1000 element generates 1.0 mW, which can induce measurable self-heating error inside small thermowells unless the input card limits excitation current to 0.1 mA or 0.2 mA.
When the symptom appears in the plant
A chemical processing plant replaced a long-distance temperature probe on a remote storage tank. The technician replaced a 3-wire Pt100 sensor with a 2-wire Pt100 probe using existing 40-meter 18 AWG copper cabling. The PLC reported tank temperature 8.5 °C higher than actual process temperature. The 3.3 Ω round-trip resistance of the 40-meter cable added directly to the 100 Ω sensor element (3.3 Ω / 0.385 Ω/°C = +8.57 °C offset error). Switching to a 3-wire Pt100 restored lead-resistance cancellation and brought measurement back within 0.1 °C.
Measuring RTD Resistance with High-Current Multimeters: Self-Heating Bias
When using a handheld digital multimeter in standard ohms range to verify an RTD on the bench, be aware of the meter's test current. Some general-purpose meters output 1.0 mA to 5.0 mA in the low-resistance (400 Ω) range. Applying high test current to small miniature Pt100 or Pt1000 elements in still air causes continuous self-heating (I²R), causing the resistance reading to steadily drift upward while probing. For accurate bench verification, immerse the probe in an ice bath (0 °C) or use a precision process calibrator designed for RTD measurement.
Five checks before replacement
- Disconnect RTD leads from the PLC input terminal block before performing resistance checks.
- Measure resistance directly across the sensor element terminals with a calibrated multimeter (compare against DIN IEC 60751 lookup table).
- On 3-wire sensors, identify the two interconnected leads (usually same color) which will read near 0.0–0.5 Ω across each other.
- Measure insulation resistance between sensor sheath and each lead wire (must exceed 100 MΩ at 100 V DC).
- Verify that the input card's line frequency filter (50 Hz or 60 Hz) matches local grid frequency to suppress AC pickup.
For cable runs exceeding 50 meters, prefer Pt1000 over Pt100 if the input hardware supports it, due to reduced lead error.
In critical custody-transfer or laboratory processes, 4-wire Kelvin connections completely eliminate lead resistance regardless of cable gauge or length.
Never splice RTD extension cables with wire nuts; always use screw terminal blocks with copper ferrules or soldered joints.
Bench checklist
- Identify the RTD baseline resistance: measure cold resistance at ~20 °C (Pt100 reads ~107.8 Ω; Pt1000 reads ~1,078 Ω).
- Verify the PLC analog input channel configuration: confirm Pt100 vs Pt1000 and 2-wire / 3-wire / 4-wire mode.
- On 3-wire RTD installations, measure lead resistance between the two common lead wires to ensure matching within 0.1 Ω.
- Check input module excitation current: ensure current does not exceed 0.2 mA on Pt1000 elements to prevent self-heating.
- Confirm cable shield is grounded at the instrument cabinet earth only, with the sensor head shield insulated.
Reference families
- IEC 60751 Standard
- NIST Monograph 175
- Fluke Process Calibration Guide
Always verify the current edition and the exact device manual for the installation.
Official references
These links point to standards bodies, industry organizations, or manufacturer documentation. Standards landing pages may require purchase or institutional access.
- IEC 60751 Industrial Platinum Resistance Thermometers IEC
Official standard for platinum RTD resistance curves, tolerance classes, and alpha coefficients.
- RTD Theory and Lead Wire Error Calculation Omega
Manufacturer application note detailing 2-wire vs 3-wire vs 4-wire resistance cancellation.
- Temperature Measurement with Platinum RTDs Fluke Calibration
Metrology reference on excitation current, self-heating errors, and calibration stability.
- SIMATIC S7 Analog Module RTD Specifications Siemens
Official manual documenting input card channel setup for Pt100/Pt1000 sensors.