Miniature Probes
General Information
Potentiometric oxygen probes developed for the exhaust gas measurements in motor vehicles (λ-probes) are frequently used in industrial equipment. Due to their construction, these probes have some disadvantages: because of the uncontrolled heating (steady working voltage) and ceramic coating of the electrodes (which increase the diffusion of special gas components) significant measuring errors can result.
The ZIROX miniature probes MS27 and SS27 with controlled heater and integrated primary electronics features high accuracy at comparatively lower costs. The main part is the approved ZIROX potentiometric zirconia-based solid electrolyte cell (drift-, calibration- and maintenance-free). The use of high-quality components and materials guarantees high long-term stability.
The SS27 was developed for trace measurements under oxidizing conditions. The MS27 was constructed for reducing conditions or oxygen concentration of more than 100 ppm. Both probe types only differ in the type of sensor element.
Applications
- Oxygen measurements in protective gases
- Exhaust gas measurements in large-scale engines
- Control optimization in small combustion plants
- Furnace gas measurements in heat treatment equipment
- Optimisation of incineration plants
- Monitozing of industrial processes under protective or inert gas atmosphere
Technical Data Miniature Probe SS27/MS27
| Installation length | 65 mm (incl. M18x1.5), 75 mm (DN40KF) |
| Diameter | 10 mm |
| Weight | 0.5 kg |
| Dimension clamp head | 64 x 58 x 36 mm |
| Protection degree | IP42, others on request |
| Power supply | 24 V DC |
| Power consumption | 17 W |
| Warm-up | approx. 5 min |
| Sensor voltage (raw signal) | 0...200 mV (0...300 mV on request) |
| Range (SS27) | 15 ppm...20.6 Vol.-% O2 (0...200 mV) 0.13ppm...20.6 Vol.-% (0...300 mV) |
| Accuracy | < 5 % rel. error |
| Measuring gas temperature | max. 300 °C |
| Probe working temperature | 700 °C |
| Surrounding conditions probe head | max. 50 °C, rel. 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 by the NERNST equation.
For normal pressure applies:
ϕ(O2) = 20.64 * e (-46.42 U/T)
- ϕ(O2): oxygen concentration in Vol.-%
- U: cell voltage in mV
- T: cell temperature in K (700 °C = 973.15 K)
- 20.64: oxygen concentration in ambient air at 50 % rel. humidity
Translation of the output signal (range 0...200mV):
| Current output 4-20 mA | 1 mA ≙ 12,5 m 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 0...200 mV range:
At a current of 5.5 mA ((5.5-4)mA x 12.5 mV = 18.75 mV) an oxygen concentration
ϕ(O2) = 8.43 Vol.-% results.
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