Vaisala INTERCAP HMDW80 SERIES Spezifikationen PDF herunterladen (Seite 14)

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Vaisala HUMICAP

®

Humidity and Temperature Transmitter Series HMT330 is a

flexible product family designed for demanding industrial applications.

cleaning agents. The chemical purge

heats the sensor at regular intervals

to remove chemicals that may have

accumulated over time.

The Importance of

Electromagnetic

Compatibility (EMC)

There are many standards defining

the ability of products to withstand

external electrical interference.

In addition, the product must not

generate emissions that can cause

interference to sensitive equipment.

Industrial applications have more

demanding EMC requirements

than HVAC installations – the CE

marking used in Europe guarantees

compliance.

Consider Wiring

and Earthing

Except for short cable runs, a

screened cable is recommended.

Proximity to high-voltage cables or

RF sources should be avoided. It is

good practice to earth the connection

cable screen at a common point and

avoid multiple earth points. Galvanic

isolation is also available on some

Vaisala products.

Which Power Supply

and Output Signals

are Needed?

The majority of measurement

instruments are powered using a low

voltage supply. If a low voltage AC

supply is used, an isolated supply is

recommended for each transmitter

to avoid earth loops or interference

from an inductive load.

Analog output instruments usually

have an option for both voltage and

current outputs. The choice depends

on the length of the signal path and

on the interfacing equipment. Some

products have a 4–20mA loop power

connection, which is a 2-wire system

where the output signal current is

measured in the supply line.

In addition to analog outputs, some

Vaisala products feature digital

communication via RS-232, RS-485,

or LAN/WLAN interfaces. Selected

commercial protocols (Modbus,

BACnet) are also available.

Consider Calibration before Purchasing

Instruments typically need to be

calibrated every year or every second

year. Calibration requirements

depend on the application and the

stability of the instrument, with wide

variations in how easy it is to carry

out field checking and calibration.

Some instruments need to be sent

to a laboratory for calibration,

for example. Understanding the

calibration needs is therefore

an important part of instrument

selection.

Calibration Frequency

An individual calibration certificate

for a particular instrument indicates

the accuracy and linearity at the time

of calibration. However, it does not

reflect the stability of the instrument

in the long run. Calibration at routine

intervals is essential to understand

the instrument’s long-term stability.

Calibration frequency depends on

the operating environment. A rule

of thumb for Vaisala instruments

is that yearly calibration is enough

for HUMICAP

®

products, whereas

in most applications a two-year

calibration interval is suitable for

DRYCAP

®

products. When measuring

in constant high humidity (>85%RH),

high temperature (>120°C), or

chemically aggressive atmospheres,

more frequent checks may be

needed.

On-site calibration of a HMW90

humidity transmitter with a HM70

hand-held meter.

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