Omega 3200ST, 3400ST manual Q1 / Q2 = K1 / K2

Q1 / Q2 = K1 / K2

Q1 is the flow rate of the new gas

Q2 is the flow rate of the original calibration gas

K1 is the K factor of the new gas

K2 is the K factor of the original calibration gas

Q1 = (K1 / K2) Q2

If K2 is larger than K1 then linear results will only be achieved if the unit does not exceed 5(K1/ K2)VDC for the full scale output.

Example 1

For a 0-200sccm unit calibrated for air the flow at 5.0VDC would be 200sccm. The K factor for air is 1. If the unit is used with Helium (K factor 1.454 relative to air) then the flow at 5VDC (i.e. the maximum flow) would be (1.454/1)200 = 290.8 sccm

Example 2

For a 0-10.0 l/min unit calibrated for Argon the flow at 5.0VDC would be 10.0l/min. The K factor for Argon is 1.45. If the unit is used with Carbon Dioxide (K factor 0.74) then the flow rate 5.0VDC would be (0.74/1.45)10.0 = 5.10l/min

The accuracy of readings using K factors is not as good as that achieved for the calibration gas. The accuracy obtained (typically ±3% for K factors similar to the calibration gas) depends on the gas being used and the flow rate.

For a list of common K Factors see Section J.

4.Changing The Flow Rate Set-Point (Using An External Voltage Source)

The required flow rate is selected by adjusting the set-point voltage. The normal control signal voltage is 0-5VDC with 0VDC corresponding to zero flow and 5VDC being equivalent to the maximum rated flow of the unit.

This input is linear and scaleable allowing different flow rates within the range of the unit to be selected. For example:

For a flow range of 0-500sccm:

A 5 VDC Input Signal would correspond to a flow rate of 500sccm If a flow rate of 300sccm were required then the set-point would be:

(300 ÷ 500) × 5 = 3.0VDC

M-4271/0707, pg. 15 of 26