Teledyne 100E, Instruction Manual

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Model 100E Instruction Manual Optional Hardware and Software
045150102 Rev XB1 51
Span gas is created when zero air passes over a permeation tube containing liquid SO
2
under high pressure, which slowly permeates through a PTFE membrane into the
surrounding air. The speed at which the SO
2
permeates the membrane is called the
effusion rate. The concentration of the span gas is determined by three factors:
• Size of the membrane: The larger the area of the membrane, the more permeation
occurs.
• Temperature of the NO
2
: Increasing the temperature of the increases the pressure
inside the tube and therefore increases the effusion rate.
• Flow rate of the zero air: If the previous two variables are constant, the
permeation rate of the into the zero air stream will be constant. Therefore, a lower
flow rate of zero air produces higher concentrations of SO
2
. The M100E usually has
a constant flow rate and a constant permeation rate, hence, variations in
concentration can be achieved by changing the IZS temperature.
NOTE
The permeation tube is not included in the IZS Option and must be ordered
separately. See Section 5.4.3 below.
Permeation Tube Heater
In order to keep the permeation rate constant, the IZS enclosure is heated to a constant
50° C (10° above the maximum operating temperature of the instrument). The IZS
heater is controlled by a precise PID (Proportional/Integral/Derivative) temperature
control loop. A thermistor measures the actual temperature and reports it to the CPU for
control feedback.
CAUTION
Gas flow must be maintained at all time for units with a permeation tube
installed. Insufficient gas flow allows gas to build up to levels that will
contaminate the instrument.
5.4.3.
IZS Permeation Tubes (Options 53, 55 & 57)
Several replacement permeation tubes are available for the IZS option. They are identical
in size and shape but are designed to have different effusion rates.
Option Effusion Rate
(± 25%)
Approximate
Concentration
Specified Flow Rate
OPT 53 421 ng/min 300 - 500 ppb 0.76 lpm
OPT 55 842 ng/min 600 - 1000 ppb 0.76 lpm
OPT 57 222 ng/min 800 – 1200 ppb 0.56 lpm
Each tube comes with a calibration certificate, traceable to a NIST standard, specifying
its actual effusion rate of that tube to within ±5% when immersed in a gas stream