Download Datasheet TKE P2O5 Moisture Cell

TKE
T
E C H N I S C H E R
K
U N D E N D I E N S T
& E
N T W I C K L U N G
NORBERT GERHARDT
Phosphorus Pentoxide Moisture Measurement Cell
For the Determination of Trace Moisture in Gases
Advantages
Low cost solution compared to cells from Ametek, Dupont or others.
Cleaning and re-coating the sensitive surface can be easily done by the operator.
TKE offers a replacement and regeneration service at an attractive fixed price.
The cells can be operated at a wide range of gas flow rates.
The standard cell comes with 1/8" Swagelok fittings, alternative fittings are free of choice.
Technical Specifications
Principle
Electrolytic cell with phosphorus pentoxide coating (also known as Keidel cell
or coulometric cell). The coating attracts water molecules from the carrier
gas which will then be dissociated electrically. The current measurable at the
electrical terminals is directly proportional to the amount of water in the
carrier gas.
Dimensions
Tube length incl. fittings 133mm (5,2"), outer diameter 22mm (0,86").
Electrical Connections 130mm (5") wires, custom configurations are available on request
Gas Flow
200 ml/min maximum
Operating Voltage
25...70V DC (dry cell)
Power Dissipation
1W maximum
Materials
Tube: Electropolished stainless steel, Sensor: Aluminium oxide ceramic with
platinum tracks, Sealing: Epoxy resin.
Refurbishment
The tube can be opened for cleaning and recoating of the P2O5 surface.
TKE Service
TKE offers the following services in conjunction with these cells:
Replacement of existing cells in analysers from Ametek, Dupont and others.
Customization of fittings and electrical connectors.
Regeneration of the cells in the TKE service lab, test certificate included.
Annual maintenance contracts: The user can always rely on having intact cells at hand.
Consulting: TKE helps you out with their expertise in moisture measurement.
Operating Instructions
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When not in use, always put caps on the
fittings while the cell is in dry condition.
Before first applying voltage, dry down the
cell 12 hours with dry carrier gas at the
rated flow. Also dry down all supplying gas
tubes.
Do not apply voltage when the cell is in wet condition as this will destroy the sensitive surface.
Do not overheat the cell. The maximum power dissipation should be limited to 1 Watt by
electronic means. Higher power will reduce the lifetime.
When opening the cell, take care not to crack the ceramic substrate of the sensor. After being
opened the cell is in wet condition due to air humidity and must be dried again.
Aggressive components in the carrier gas can be used as long as they don't react with P 2O5.
Esp. Ammonium (NH4+) should be avoided.
Oxygen in the carrier gas affects the results because of recombination.
From time to time check the sensitivity with a reference sample.
If the cell becomes insensitive it needs to be regenerated. This is best done by TKE, a
comprehensive test protocol is included.
Modes of Operation
The TKE Cell can be used in either one of two modes of operation:
1. In the absolute measurement mode,
mode the gas flow is slow enough, so the entire water will be
dissociated by the active surface before the carrier gas reaches the end of the cell tube. The
electrical charge needs to be counted by integration of the current, it is directly proportional to
the count of water molecules. Two electrons are needed to split up one water molecule. Due to
this simple principle a calibration of individual cells is not necessary. The gas flow does not
need to be observed as long as it stays below the limit where all molecules can be absorbed
(none are leaving the cell). The operating voltage has an influence on the response time but not
on the absolute amount of detected water.
2. In the dynamic equilibrium measurement mode,
mode the gas flows fast through the cell. Only a
fraction of water molecules will be absorbed by the P 2O5 surface while the rest is leaving the
cell. In this case the electrical current has a relation not only to the concentration of water, but
also to the pressure and the flow rate. For this reason the cell should be operated at controlled
pressure and flow rate to get comparable results. A cell constant (relation between water
content and current) needs to be determined for each individual cell. The cell constant will drift
over the lifetime, so it needs to be recalibrated regularly. The voltage applied has no influence
on the current but on the response time to changes in the water concentration.
TKE
Norbert Gerhardt
Schlappmühler Pfad 45
DE-61250 Usingen
Germany
tel +49 (0) 6081 - 67822
mobile +49 (0) 160 - 8429038
email [email protected]
web www.t-k-e.com
VAT ID Nr. DE232539797
Release date: 2016-05-16