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Simply Smart: The Hydrogen Sensor for Chromatographic Systems

The DVLS3 Simply Smart Hydrogen Sensor

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

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

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

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%

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

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

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

Gas sensitivity Hydrogen Sensor

Typical Zero Offset drift with Temperature Hydrogen Sensor

Typical long term zero offset drift Hydrogen Sensor

Typical long term gas sensitivity drift Hydrogen sensor

Hardware overview for a Hydrogen Sensor for GC applications

Sensor installed in the GC Oven

Transfertube through the oven wall to ensure a stable temperature

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.

After 1% H2 detection, the sequence will stop after the analysis. No waste of analyses or sample.

Automatic Stop Signal to GC

After 1% H2 detection a choice of alarm signals:

17

Alarm messages

§  Acoustic alarm

§  Optical alarm (blinking display)

§  SMS alarm message

Calibration & Maintenance

§  Zero Point Calibrated Using Air

§  Alarm level Calibrated using Calibration Mixture

§  Yearly or after maintenance or repair

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

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.