Future Design MCTB 4.3, Руководство пользователя

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MCTB
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We do not want to delay the start of the compressor too long, so as shown above s short delay of 10 second is
used. The equation shown above defines the condition at which the time delay begins. Since we do not want
the compressors activating unless the chamber is on, we begin with the chamber event (S1_EvOut3) having to
be on which is loop 1 event output 3. As long as that event is on, we require the compressor to run if cooling
is required. Thus, we add the condition of loop 1 output being less than -1% which is a cooling demand of 1%
(S1_%Out < -1). We also need the compressor to activate if the humidity system is on and dehumidification is
called for. This is loop 2 event output 3 active and loop 2 output being less than -1% which is a dehumidification
demand of 1% (S2_EvOut3 AND (S2_%Out < -1)).
Note that the two conditions for cooling and dehumidification have to be combined with a logical OR in
parenthesis so that if the chamber event is on AND cooling OR dehumidification are required the timer will be
activated. The position of parenthesis is important so that the evaluation is carried out properly. As can be
seen, the equation can become complicated when multiple evaluations are required so it is best to write out the
equation first and then enter it into the MCTB. Now that we have the start delay, we need the stop delay. We
will advance to math/logic equation 2 and define it as a Timer type also.
Like the start delay, we need the MCTB to continuously
monitor system operation so the Trigger is “Always”.
The Tagname can be “CMP OFF DLY” so we know it determines when the compressors are to turn off. We
also want to extend the off delay so that once set point is reached, they will be available for a small bump of
cooling or dehumidification should it be needed frequently to maintain set point, so in this example we will use
90 seconds. The off delay is essentially the opposite of the on-delay equation. We want the compressors to
turn off when both cooling AND dehumidification are not required.
As shown in the image below, we begin by evaluating the loop 1 percentage of output and when greater than
1%, we want to signal that the compressors are not required (S1_%Out > 1). However, we must also perform
a logical AND with the dehumidification requirement because we do not want the compressors turning off unless
both cooling and dehumidification are not required. The dehumidification requirement is also only a valid
condition if the humidity system is on. If it is turned off, the dehumidification requirement does not matter as
the humidity system is not enabled. Thus, our off delay can time down if the humidity event is not active OR
the loop 2 is actually calling for humidity (NOT S_2EvOut3 OR (S2_%Out > 1)).
Again, note the importance of the parenthesis in evaluating the cooling requirement, the dehumidification
requirement, and then evaluating the two together to determine if the off-delay timer can count down.
Before utilizing the on and off delay timers in logic equations to active the compressor outputs, one more timer
is required. In the case of dual stage refrigeration systems, a delay is required between the start of stage 1 and
the start of stage 2. This is necessary in order for the first stage to be ready for the load placed on it when the
second stage starts, so that it can remove the heat from the second stage. Thus, we require one more timer
which will create in math/logic equation 3.