Ahlborn ALMEMO 2390-5 Servisní příručka stáhnout pdf (Strana 4)

Thermoanemometer

3.5.2 Thermoanemometer

Thermistors and hot-wire anemometers are highly sensitive sensors that can

also measure very small air velocities. They are suitable for use in all fields of

air conditioning, ventilating, indoor applications and measurements at working

places (draft). The ALMEMO

sensor range provides thermoanemometer

probes for different measuring ranges and measuring accuracies:

• Thermoanemometer FV A645-THx with plug-on module housing

and fixed measuring range.

• Thermoenemometer MT 84x5 with separate housing for electronics,

ALMEMO

connecting cable and selectable measuring range.

The measuring variables, temperature (FVA935-TH) and air velocity are pro-

grammed within the ALMEMO

sensor connector on two measuring channels.

They can be activated and displayed with the correct scaling and dimension by

every ALMEMO

measuring instrument. For volume flow rate measurements

the cross section or the diameter of the ventilating shaft can be easily entered

into ALMEMO

hand-held devices.

Measuring Principle

A temperature-dependent semiconductor

(NTC) is integrated in the measuring

probe and is heated by a current.

The heated semiconductor cools down

as soon as it is exposed to an air flow.

The amount of heat loss is a measure for

the air velocity. A control circuit keeps the

temperature of the element, which has

cooled down by the air flow, on a con-

stant value. The control current is propor-

tional to the flow velocity.

3-5-4 ALMEMO

Sensors

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Ahlborn ALMEMO 2390-5 Servisní příručka Strana 4