Simply Smart: The Hydrogen Sensor for Chromatographic Systems
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Transcript of Simply Smart: The Hydrogen Sensor for Chromatographic Systems
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www.davinci-ls.com
Simply Smart: The Hydrogen Sensor for Chromatographic Systems
The DVLS3 Simply Smart Hydrogen Sensor
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Content
§ Four reasons for using H2 as a carrier gas § Safety measures § Hydrogen sensor § Principle of operation and measurement § Hardware overview § Calibration and maintenance § Summary § Questions
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1. Fast Analysis: § Fast diffusion rate; 4 times
faster than N2 § Half as viscous as helium;
higher linear gas velocity and shorter retention times
2. High Efficiency:
§ Flattest Van Deemter curve
Reasons for using H2 as a Carrier Gas
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3. Prolonged Column Life:
□ Some applications have a lower elution temperature, therefore the column life is longer
4. Cost effective: □ 3x’s less expensive than its helium equivalent □ Bottle or generator
Reasons for using H2 as a Carrier Gas
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Reluctant to use H2 as a Carrier Gas?
§ Hydrogen is an Explosive Gas: Undetected gas leaks can lead to an explosion in the GC oven
§ LEL of hydrogen in Air is at 4%
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Safety measures § Monitor hydrogen usage § Safety measures in GC hardware □ Safety Shutdown: when gas pressure set points
are not met, the valve and heater are shut off to prevent explosion
□ Flow Limiting Frit: if valve fails in open position, inlet frit limits the flow
□ Oven ON/OFF Sequence: Fan purges the oven before turning on heater to remove any collected H2
□ Explosion Test: GC designed to contain parts in case of explosion
§ Hydrogen sensor in the oven or valve box
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Principle of Operation Hydrogen Sensor
§ Catalytic combustion by catalytized resistor or “pellister”
§ Surface of the pellet acts as a catalyst when hot
§ Exothermal oxidation of flammable gases ú 2 H2 + O2 → 2 H2O(g) + heat
§ Temperature rise results in a change in the electrical resistance
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Principle of Measurement Hydrogen Sensor
§ Compensator pellet is identical but without catalyst
§ Compensator pellet removes the effect of environmental factors
§ Measurement circuit: a Wheatstone Bridge
8 13 March 2013
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Gas sensitivity Hydrogen Sensor
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Typical Zero Offset drift with Temperature Hydrogen Sensor
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Typical long term zero offset drift Hydrogen Sensor
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Typical long term gas sensitivity drift Hydrogen sensor
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Hardware overview for a Hydrogen Sensor for GC applications
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Sensor installed in the GC Oven
Transfertube through the oven wall to ensure a stable temperature
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Automatic Switch to Nitrogen After 1% H2 detection, the carrier gas supply is switched to nitrogen. The system will maintain a flow through the column.
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After 1% H2 detection, the sequence will stop after the analysis. No waste of analyses or sample.
Automatic Stop Signal to GC
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After 1% H2 detection a choice of alarm signals:
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Alarm messages
§ Acoustic alarm
§ Optical alarm (blinking display)
§ SMS alarm message
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Calibration & Maintenance
§ Zero Point Calibrated Using Air
§ Alarm level Calibrated using Calibration Mixture
§ Yearly or after maintenance or repair
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Summary (1)
§ Catalytic Pellistor gas specific sensor, linear range
of 0-2% H2 (0-50% LEL)
§ Unaffected by humidity, stable output for long
periods, more resistant to shocks and vibrations.
§ Expected lifetime: over five years
§ Long term stability drift sensitivity: less than 2mV
§ User defined alarm: optical, acoustic and/or SMS
up to 50% LEL
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Summary (2)
§ Instrument readings: provide real time sensor
readings with alarm levels, channel states
§ Valve : High pressure 3 way solenoid valve
§ Oven operating temperature: up to 450◦C
§ Multiple Sensors: Max 4 sensors individually
controlled
§ Sensor options: temperature, barometer, level,
oxygen or hydrogen as a leakdetector.