Vaisala DRYCAP DM70 User's Guide download pdf (Page 19)

Chapter 4 _____________________________________________________ Dewpoint Measurement

CHAPTER 4

DEWPOINT MEASUREMENT

The following recommendations should be taken into account when

measuring in very dry environments.

- A clean environment is always best for humidity measurements.

- The number of connections should be minimized to avoid leaks.

- The flow rate must be adequate.

- Dead ends must be avoided as they cannot be flushed easily.

- The tube temperature must never lie under the dewpoint of the

sample gas. This may lead to condensation and false results.

- The sample tubing should be of as short length as possible. The

surface area should be minimized using the narrowest tubing that

the flow conditions allow.

- The surface finish of the pipework is important. Polished or

electro-polished steel is recommended for best results.

- Hygroscopic materials should be avoided in the sampling lines. Use

stainless steel membranes instead of rubber membranes.

- Impermeable materials should be selected to avoid inward diffusion

of moisture through the sampling tubes and enclosures. Such

impermeable materials are, for example, high-quality stainless steel

and metals. Avoid PVC or nylon tubes.

Measuring

If you start DM70 for the first time, see section Preparations Before

Use on page 13. Otherwise, follow the instructions below.

1. Connect the probe to the MI70 indicator.

2. Press the Power On/Off button.

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Vaisala DRYCAP DM70 User's Guide Page 19