Teledyne 356WA instruction manual Pmm-Hg = 760 2.50 per 100 ft. of altitude

Appendix Model 356WA

or by knowing the altitude

P(mm-Hg) = 760 - (2.50 per 100 ft. of altitude)*

The vapor pressure of water at ambient temperature can be obtained from Table 1.

To determine the corrected flow (Fcorrected), substitute the ambient tem- perature, pressure and vapor pressure of water in the following formula:

Fcorrected	⎛	T	⎞		760 mm Hg	⎛	P + P	⎞
	= 150 cc min × ⎜		⎟	×	P	× ⎜	water ⎟
	⎝	294° K * * ⎠				⎝	P	⎠

Where:

T = ambient temperature (in °K) P = ambient pressure (in mm Hg)

Pwater = vapor pressure of water at ambient temp. (in mm Hg)

By way of example, suppose that the target’s position on the flow tube is in question and it has been determined that the ambient temperature is 77 °F and the altitude where the instrument is being used is 5000 ft. above sea level.

Ambient Temp: ° K = 5 (77 − 32) + 273 = 298° K 9

Ambient Pressure: P(mm Hg) = 760 - (2.50 × 50) = 635 mm Hg

Vapor Pressure of Water (at 298° K): 23.9 mm Hg

Corrected Flow: Fcorr = 150 ×	298		760	⎛	635 + 239.	⎞	= 189 cc min
	294	×	635	× ⎜	635	⎟
				⎝		⎠

*This approximation is within ±0.5% of the ICAO Standard Atmo- sphere over the range 0-7500 ft. above sea level. Ref: “Fluid Mechanics for Engineering Technology” by Irving Granet, Prentice Hall, pp 83–84.

**Reference ambient temperature : 294 °K (21 °C) was the ambient temperature used in the Faradaic calculations.

A-6 Teledyne Analytical Instruments