EZT-570S User Manual
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Process:
This mode
uses the lower and upper set points as the upper and lower range of the air
temperature set point. The output of the product control loop is then used to calculate a
linear set point between these two values in order to provide the set point for the air
temperature loop.
The deviation mode has the benefit of limiting the maximum and minimum temperature that the air
can achieve relative to the desired product set point. This allows the system to be fine-tuned to the
minimum amount of overshoot required to obtain the desired product temperature.
The process mode has the benefit of maximum change rates by allowing the air temperature to go to
absolute limits. This allows the product to achieve set point temperature as quickly as possible, but
does so at the cost of stability. If the part has a large thermal lag, the air temperature control may
oscillate uncontrollably once the product reaches set point because of the large overshoot. In most
cases, deviation control is the recommended selection.
The product control feature can be turned on and off in one of two ways. It can be either enabled or
disabled by pressing the desired mode control button, disable, deviation or process, or an event can
be used to enable and disable the selected mode when the “uses event” button is chosen in addition
to the product control mode.
Uses Event:
When this selection is made, the selected product control mode (deviation or
process) is turned on and off with the product control event (chamber event 10).
When the selection is not made, the selected product control mode is in operation at
all times until disabled by the user.
The uses event selection for enable/disable allows product control to be turned on and off
during different steps of a ramp/soak program or manually from the Overview screen or
Manual Operation window on the Main view without having to disable it altogether. This can
be a useful function for varying product testing in which specific programs are used for
different product tests. It allows a program, where product control is required, to turn it on
through the event when run, and does not require the operator to insure that the correct
control mode is selected.
5.5.1
Using Product Control
The key to using product control, or even if it is necessary for your testing purposes, is understanding
your product and what temperature conditions you want to test it under. There are several other
factors that also come in to play such as the product shape, location in the chamber and most
importantly, air flow over the product.
5.5.1.1
Should I Use Product Control for My Test
It is important to remember that it is the chamber air that is adding or removing heat from your
product, and there must be a difference in temperature between them in order to do this. The larger
this difference, the more heat that flows. Additionally, the more air moves across your product, the
more heat can be added or removed at any given temperature difference.
Product placement in a chamber can affect the rate at which product changes temperature. It is
important to not overload a chamber since blocking or restricting airflow will reduce performance and
can prevent some of the product from seeing the proper test conditions. Product should be located in
such a way that it gets good air distribution around it. While this may not be always possible due to
certain circumstances, such as product shape, it is a factor to consider whenever possible.
Summary of Contents for EZT-570S
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