Despatch RFD1-42 -2E with Protocol 3 - Manual (Page 16)

T HEORY OF O PERATION RFD1-42-2E Oven Owner’s Manual
16 Version 1
Copyright © 2012 by Despatch Industries.
All rights reserved. No part of the contents of this manual may be reproduced, copied or transmitted in any form or by any
means including graphic, electronic, or mechanical methods or photocopying, recording, or information storage and
retrieval systems without the written permission of Despatch Industries, unless for purchaser's personal use.
Damper Control
The chamber cannot readily dissipate heat generated by friction without a fully open fresh air
damper. With the fresh air damper fully open, the thermal equilibrium temperature is the mini-
mum operating temperature of the chamber.

When the damper is in full open position, the oven may not be
able to heat to the maximum oven operating temperature.
3.2.1.3. Other Damper Settings
Damper settings can take distinct operating positions other than full closed or full open. In most
cases, uniformity and cool-down rates influence damper settings.
Chamber Uniformity
The system’s inside chamber pressure influences chamber uniformity. Pressure inside the
chamber depends on the amount of fresh air flowing into the chamber. When a large volume of
fresh air flows into the chamber, the chamber pressurizes slightly and overall temperature
uniformity improves. The slightly pressurized chamber produces the effect of "pushing" air to the
corners of the chamber. Typically the corners of the chamber improve with respect to temperature
distribution while the core of the chamber maintains excellent uniformity characteristics
regardless of damper position.
Pressurization of the chamber typically is a factor when the chamber is loaded heavily. The best
uniformity results, with respect to the product, are achieved when no more than two-thirds of any
inside chamber dimension are used. The best overall results are achieved when the product(s) are
located in the center of the chamber.
Cool-Down Rates
The more open the damper, the faster the cool-down.
3.2.1.4. Exhaust Damper Control
Adjusting the exhaust damper (Figure 4) aids in pressurizing
the chamber.
3.3. The Protocol 3 Controller
The Protocol 3™ controller is a microprocessor based digital
temperature controller designed for simple and flexible oven
operation (Figure 5). The Protocol 3 controller operates as a
dual-functioning controller/High Limit instrument. The control portion utilizes a time
proportioning voltage signal to control heating devices with minimal temperature fluctuations.
The High Limit portion protects the product and/or the oven from overheating. If the product
being processed has a critical high temperature limit, the High Limit setpoint should be set to a
temperature somewhat below the temperature at which the product could be damaged. If the
Figure 4. RFD1-42-2E Oven Exhaust
Damper Control