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Choosing the Best Gas Detector - Sample Draw vs. Diffusion

Sample-Draw vs. Diffusion

Sample-Draw vs. Diffusion
  • Drawbacks of diffusion only designs:
    • Instrument only able to monitor the atmosphere in the immediate vicinity of sensors
    • Only way to obtain readings from remote location is to lower the instrument by rope or lanyard into the confined space
    • Not possible to use monitor for "pick hole" sampling (requires additional hand aspirator sample draw kit or motorized pump)
  • Drawbacks of sample-draw only designs:
    • Sample lag time: instrument cannot detect contaminants until they reach the sensors
    • Potential for leakage in the system: critical to test system for leakage prior to use
    • Potential for pump malfunction: some instruments only operable as long as pump functions
Sample-Draw vs. Diffusion

Optimal design

Optimal design
  • Instrument can be used in either diffusion or sample draw mod
    • "Shuttered" pump designs allow instrument to be used in diffusion mode without having to remove the motorized pump
  • Motorized pump has its own power supply
    • "Parasitic" type pumps are powered via the instrument battery, reducing operation time per charge
  • Motorized pump is diaphragm type design
    • Improves pump flow rate and maximum remote sampling distance

Hand-aspirated sample-draw kit

  • Available for all models of diffusion type multi-gas instruments
  • Make sure to squeeze the bulb the required number of times for sample to reach the sensors
  • Continue to squeeze bulb until readings are stable
  • Make sure to test the system for leakage prior to use:
    • Block end of the sample tubing or probe with finger
    • Squeeze the aspirator bulb
    • Bulb should stay deflated until blockage is removed
Hand-aspirated sample-draw kit