The Interscan Monitor Newsletter > Volume 2, Number 3

Volume 2, Number 3

WELCOME.....

This issue of the MONITOR is heavy on content--even if it is not exclusively about Interscan...

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APPLICATIONS 'R' US

I've often said that 90% of gas detection is calibration. Most of the other 10% consists in knowing the application details.

Although we don't do a lot of stack monitoring, this one did come up recently, so I'll share it with you:

The requirement was to monitor sulfur dioxide coming out of a process. The sample temperature was 95 degrees F (35 deg C), and the relative humidity was 7 percent. Since SO2 is quite soluble, it is important to prevent uncontrolled condensation of water.

Relative humidity, although frequently used in specifications, is not a very useful parameter, as you will soon see. A much better measurement is the dew point.

For you non-chemists, dew point is the temperature at which condensation will occur. For this to happen, the partial pressure of water in the air must equal the equilibrium vapor pressure of water at that temperature. In this condition, the relative humidity equals 100 percent.

The relative humidity at a given temperature (T) equals... the partial pressure of water at T, divided by the equilibrium vapor pressure of water at T.

This quotient is expressed as a percent.

Relative humidity (RH), then, is a function of temperature. That's why it isn't very useful in this context.

We must calculate the dew point of the stack sample.

At 95 deg F (35 deg C), the vapor pressure of water is 42.175 mm Hg. (look up in Handbook of Chemistry and Physics)

A 7% RH means that the partial pressure of water is 2.95 mm.

Referring to the same tables, 2.95 mm is the vapor pressure of water at -6 deg C (21 deg F).

Thus, given the stack sample in question, condensation would occur at -6 deg C (21 deg F).

Since the ambient temperature will likely go below -6 deg C at this location, provisions will have to be made to either heat trace the sample tubing, or remove water.

In this case, we recommended a Perma Pure Dryer to lower the dew point, allowing the sample to be transported without fear of condensation.

A competitor suggested that a diffusion sensor be placed in the stack!! At the concentrations of SO2 expected, the sensor would have lasted about three days.

Know and understand your applications, or find a supplier who does.

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KEYBOARD SHORTCUTS AND TRICKS FOR WINDOWS 95

***Cut and Copy Across Many Applications***

You can use the keyboard shortcuts of Ctrl+C to copy, Ctrl+V to paste, and Ctrl+X to cut, across even programs that don't have the option in the menus. If you make any mistakes, you can also use Ctrl+Z to undo.

***FAST System Properties***

For those of you who like to dabble with individual device managers and hardware profiles, and have a keyboard with the Windows key on it, here is a badly documented shortcut to the system properties dialog box. Just hold down the Windows key and press Pause/Break. This is much faster than going to My Computer, Control Panel, System...

***Lock Warning***

Do you ever accidentally hit the Caps Lock or the Num Lock key by mistake, only to realize a few words later that what you have written is not what you wanted? Windows 95 has an option to let you know when either of these keys have been hit. Open the Control Panel, choose Accessibility Options, and select Use Toggle Keys. Click OK, and now every time you hit Caps Lock or Num Lock, you will hear a warning tone.

***Quick Top and Bottom***

To get to the top of a folder window or most files quickly, press Ctrl+Home. To get to the bottom, press Ctrl+End.

***Selecting All Files***

To select all files in a folder, or all the content of an open file, press Ctrl+A

***Windows Key Features***

The windows key on the Win95 keyboard can serve more purposes than just clicking the start button. Hold down the Windows key and press one of the following keys to start the applications: e = explorer, f = find, m = minimize all windows, r = run.

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DEMO SOFTWARE TO TRY OUT

***IH Services Calculator Demo***

IH Calculator is designed to automate calculations commonly used by industrial hygienists.

The calculations are grouped under the menu headings of:

*Air Sampling
*Engineering
*Ventilation
*Noise
*Heat
*Stress
*Radiation
*Statistics

IH Calculator also includes, under the Tables menu, the following useful information:

*A periodic table
*A units conversion table
*A table of physical constants
*A table of PELs, including molecular weight, specific gravity, and CAS numbers.

Download Windows Demo (1.3Meg) ftp://www.acgih.org/acgih/ihdemo.exe

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Until next time, I remain

Your faithful webmaster

 P.O. Box 2496 • Chatsworth, CA 91313-2496
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