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3000 Series - Application Notes on Restrictors, Pressures, and Flow Recommendations

3000 series analyzers require reasonably regulated sample pressures. While the 3000 analyzers are not sensitive to variations of incoming pressure (provided they are properly vented to atmospheric pressure) the pressure must be maintained as to provide a useable flow rate trough the analyzer. Any line attached to sample vent should be 1/4 or larger in diameter.

A usable flow rate for a 3000 series analyzer is one which can be measured on the flowmeter. This is basically .2 - 2.4 SLPM . The optimum flow rate is 1 SLPM (mid scale). Note: response time is dependent on flow rate, a low flow rate will result in slow response to O2 changes in the sample stream. The span flow rate should be the approximately same as the sample flow rate.

The sensors used in 3000 series analyzers are optimized to function at atmospheric pressure. At pressures other than atmospheric the diffusion rate of O2 will be different than optimum value. Higher pressures will produce faster O2 diffusion rates resulting in higher O2 reading and shorter cell life. To use a 3000 series analyzer at a cell pressure other than atmospheric, the analyzer must be calibrated with a known calibration gas at the new cell pressure to adjust for the different diffusion rate. Cell pressures below 2/3 atmospheric are not recommended because as they tend to cause excessive internal expansion which may result in seal failure.

For operation at cell pressures other than atmospheric care must be taken not to change the sample pressure rapidly or cell damage may occur. For cell pressures above atmospheric, caution must be exercised to avoid over pressuring the cell holder. ( percent analyzers will require some type of cell retainer to prevent the cell from being pushed out by the pressure .) For operation at pressures below atmospheric pressure a suffix C ( clamped) cell is required.

For proper operation, all 3000 series analyzers require a flow restriction device. This device is typically a restrictor or a valve. This restriction device serves two functions in the sample path. The first function is to limit the flow rate of the sample through the analyzer. A restrictor is chosen to operate over a range of pressures and provide a useable flow rate over that range.

The second function that the restriction device provides is a pressure drop. This device is selected to provide the only significant pressure drop in the sample path.

The current revision of the 3000 series analyzers are supplied with a kit containing two restrictors and a union which are user installed. These parts supplied to give the end user more flexibility when installing the analyzer. The restrictor kit is suitable for high and low positive pressure applications as well as vacuum service ( atmospheric pressure sample) applications ( see manual for installation instructions).

The standard restrictor ( BLUE DOT ) is recommended for pressures between 5 PSIG and 50 PSIG. For positive low pressure application ( 5 psig or less ) the un-marked restrictor is better suited . For none pressurized sample applications the marked restrictor should be used and configured for vacuum service. Note: for extremely low positive pressure applications ( less then 2 psig) the vacuum service configuration should provide higher performance ( higher flow rates). For vacuum service the end user must supply a vacuum pump and a by-pass valve for the pump. A vacuum level of 5 - 10 inches of mercury should provide the optimum flow rate.

CAUTION: flow restrictors have very small orifices and may be plugged by small particles ( .005 dia or larger) A sample filter must be included in the sample line prior to the restrictor! ( a 60 micron filter is recommended)

Example 1
with a incoming pressure of 10 psig the std restrictor (blue dot) will provide a flow rate of .76 SLPM. Up-stream of the restrictor the sample line pressure will be 10 psig, while down stream ( including the cell) the pressure will be at atmospheric pressure.( analyzer vented to atmospheric pressure) Note, all other pressure drops in the sample path are insignificant at these flow rates. This insures that the cell operates at atmospheric pressure. At very high flow rates ( off scale of flow-meter), pressure drops other than the restriction device could become significant , and result in pressurizing the cell.

Example 2
A 3000TA is configured for vacuum service as follows. The un-marked restrictor is placed in the sample vent port. The down stream end of the restrictor is then connected to a vacuum pump and by-pass valve. The by-pass valve is adjusted to provide a flow rate of 1 SLPM. The sample pressure between the pump and the restrictor will be approximately -7 inches of mercury, while the pressure in the balance of the sample system including the cell will beapproximately at atmospheric pressure (provided the sample flow into the analyzer is not blocked.)

To improve the system response, a by-pass can be added to increase the sample flow rate to the analyzer by a factor of ten. A by-pass provides a sample flow path around the analyzer of 2 - 18 SCFH. typically.

3000 series analyzer requirements for units with Auto-Cal options. The customer must supply a control valves (or restrictors) for any SPAN or ZERO gas source which is attached to the Auto-Cal ports. The valve should be adjusted to the same flow rate as the sample gas . When restrictors are used, the gas pressure must be adjusted to achieve the proper flow rate.

Operation without a restrictor device is not recommend as mentioned above. A 3000TA without any flow restrictor device was tested on 11-19-97. This results in a flow rate of 2.4 SLPM @ 1 PSIG. This is a cv of 0.023 for the standard sample system.


1 PSI = 2.04 INCHES OF MERCURY (in. Hg.)
1 SCFH = 0.476 SLPM

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