Eurotherm 2604/2704 l' Owner's Manual

2704 2604

MODEL

Humidity control supplement

Ideal for:

•

Reliability testing

•

Climatic simulation

•

Culture & plant growth

•

Simulated altitude control

Environmental chamber control

The 2704/2604 is ideal for use in applications where it is necessary to simulate the environmental conditions of temperature, humidity and sometimes altitude. Control of these conditions require certain unique features from a controller. Firstly, the controller needs to be able to generate a setpoint profile. This feature allows the user to predefine a series of setpoint changes. Secondly the controller needs to be able to measure humidity using either the traditional

Wet/Dry bulb method or by interfacing to solid state sensors. The controller may also be required to turn a refrigeration compressor on and off, operate a bypass valve, and possibly operate two stages of heating and/or cooling (see diagram below).

The 2704/2604 is able to provide these functions.

Features:

•

Synchronised setpoint profiles

•

%RH & dewpoint measurement

•

Altitude compensation

•

Compressor timer

Pressure

Probe

Temperature

Probe

T P H

Humidity Probe

Humidity output

Vent

Vacuum pump

Cooling output

Sprinklers

Cooling

De-humidify

Heaters

De-humidify output

Vent output

Pressure output

Environmental chamber abc

Temperature control

The temperature of the environmental chamber is controlled via a single loop with two control outputs. The heating output time proportions electric heaters, usually via a solid state relay.

The cooling output normally operates a refrigerant valve which introduces cooling agents into the chamber. The 2704/2604 has an advanced PID control algorithm which automatically calculates when heating or cooling is required. Additional stages of both heating and cooling can also be implemented if required.

Humidity control

Humidity in a chamber is controlled by adding or removing

Water vapour. As with the temperature control loop, two control outputs are required(i.e.Humidify and Dehumidify). The humidity output regulates the amount of steam allowed into the chamber, adding steam increases the humidity level. Water vapour is added by either a boiler, evaporating pan or by direct injection of atomised water.

· Evaporating pan of water warmed by a heater regulates the humidity level by controlling the temperature of the water.

· Atomisation system uses compressed air to spray water vapour directly into the chamber. The same compressor used for cooling the chamber accomplishes dehumidification. Different sets of ‘heat’ exchanger coils are used along with a different control valve.

Altitude control

Altitude is simulated by controlling the pressure inside the chamber. Usually a vacuum is drawn to simulate high altitudes.

If the application requires simulating altitude at sea level and the chamber is located at an altitude higher than sea level, then the chamber must also be pressurised. Again, a two channel output controller is required. Pressure varies nonlinearly with altitude so the pressure signal must have a special linearisation applied to it.

Compressor control

Another requirement of the controller is to be able to start and stop the cooling compressor. To alleviate wear and tear caused by cycling the compressor, the chamber controller will turn the compressor on and leave it on whenever cooling or dehumidification is required. The compressor will usually be kept running for 5 to 15 minutes after cooling has stopped. If the controller starts to call for cooling again the “compressor timeout” timer deactivates until cooling is called for again.

Wet RTD

Humidity

Control Loop

Humidity

Dehumidity

Dry RTD

Humidity

Function

Block

Compressor

Timer

Compressor Start

Pressure

Temperature

Control Loop

Altitude

Control Loop

Heating

Cooling

Increase

Decrease

Run

Hold

Reset

Setpoint

Programmer

Typical environmental chamber controller

EUROTHERM LIMITED http://www.eurotherm.co.uk

email: [email protected]

UK SALES OFFICE

Eurotherm Ltd

Faraday Close Durrington Worthing BN13 3PL United Kingdom

Sales and support: Tel. +44 (0)1903 695888 Fax +44 (0)1903 695666

Sales and support in over 30 countries worldwide

Enquiries/orders to:

Eurotherm Ltd Faraday Close Durrington

Worthing BN13 3PL United Kingdom

Tel. +44 (0)1903 268500 Fax +44 (0)1903 265982

© Copyright Eurotherm Controls Limited 2000

All rights strictly reserved. No part of this document may be stored in a retrieval system, or any form or by any means without prior written permission from Eurotherm

Controls Limited. Every effort has been taken to ensure the accuracy of this specification. However in order to maintain our technological lead we are continuously improving our products which could, without notice, result in amendments or omissions to this specification. We cannot accept responsibility for damage, injury loss or expenses resulting therefrom.

Part No. HA026748 Issue 1.1

Printed in England 01.01