Properties
The ZIROX® Miniature Probe SS27 is a potentiometric oxygen probe designed for exhaust gas measurements. It addresses common issues found in traditional probes, such as uncontrolled heating and ceramic electrode coatings, which can lead to measurement errors. The SS27 features a controlled heater and integrated primary electronics, offering high accuracy at a low cost. It utilizes a zirconia-based solid electrolyte cell that is drift-, calibration-, and maintenance-free, ensuring long-term stability.

Applications
The SS27 is used for exhaust gas measurements in large-scale engines, process control, and combustion optimization in small-scale firing equipment. It is also applicable for furnace gas measurements in heat treatment equipment, optimization of incineration plants, and monitoring industrial processes under protective or inert gas atmospheres.

Technical Data
- Length: 50–300 mm
- Diameter: 10 mm
- Weight: 0.5 kg
- Dimension clamp head: 64 x 58 x 36 mm
- Protection degree: IP42 (others on request)
- Mounting variants: KF25, KF40, screw thread M18 x 1.5
- Power supply: 24 V DC
- Power consumption: 17 W
- Warm-up time: Approx. 5 min
- Sensor voltage (raw signal): 0–200 mV (0–300 mV on request)
- Range: 15 ppm–20.6 vol% O2 (0–200 mV), 0.13 ppm–20.6 vol% (0–300 mV)
- Accuracy: < 5% relative error
- Measuring gas temperature: Max. 300 °C
- Probe working temperature: 700 °C
- Surrounding conditions probe head: Max. 50 °C, relative humidity < 80%
- Offset: Approx. -2–-8 mV (compensable)
- Output signal: 4-20 mA (0-5 V, 0-10 V on request)

Plug Assignment
1. Analog output + IA
2. Analog output GND IA
3. Power supply GND VB
4. Power supply + 24 V VB
5. Relay RDY

Calculation of Oxygen Concentration
The oxygen partial pressure is calculated using the NERNST equation: ϕ(O2) = 20.64 * e^{(-46.42 U/T)}, where ϕ(O2) is the oxygen concentration in vol%, U is the cell voltage in mV, and T is the cell temperature in K (700 °C = 973.15 K).

Translation of Output Signal
- Current output 4-20 mA: 1 mA = 12.5 mV cell voltage
- Voltage output 0-5 V: 1 V = 40 mV cell voltage
- Voltage output 0-10 V: 1 V = 20 mV cell voltage

Example: For a 0–200 mV range, at a current of 5.5 mA ((5.5-4)mA x 12.5 mV = 18.75 mV), the oxygen concentration ϕ(O2) = 8.43 vol%.