LB-762 Controller Installation Manual
LAB-EL
Important
For operation of collective measurement of external air parameters it is necessary to ensure ongoing operation of the
control software on a PC computer.
1.7
Collective CO
2
concentration measurement
In the measuring system consisting of more regulators (both LB-762 and LB-760), it is possible to ensure CO
2
concentration
measurement in two ways:
• local measurement – each regulator has its own individual CO
2
meter,
• collective measurement – one CO
2
meter covers more cultivation halls.
Connecting individual CO
2
meters is relatively costly, the application of collective measurement permits reduction in instal-
lation costs. Figure
presents the scheme of a typical installation of collective CO
2
measurement. The system consists of
the following elements:
• CO
2
meter – used for CO
2
concentration measurement in the air supplied from different halls,
• pump – provides air suction from different halls,
• valves – provide opening of air supply from different halls.
Rysunek 1.6: Scheme of a collective system of CO
2
concentration measurement
The whole operates as follows: the system opens valves in cycles for different halls, accepting at a given moment air only
from one hall. The pump sucks in air for a given time and delivers it to the meter of CO
2
concentration (the suction time is
dependent on the length of pipes supplying air). After the specified time has elapsed, one may consider that air which has
arrived to the meter corresponds to that in the hall and the CO
2
meter makes the final measurement whose result is sent to
the regulator controlling the relevant hall. Then, the air supply valve for the particular hall is shut down, and opened is the
valve for the next hall. The whole continues in cycles.
Additionally, it is possible to incorporate to the system CO
2
concentration measurement for external air. This has two
functions: periodic ”blowing” Of the CO
2
meter with fresh air with low CO
2
concentration and verification of correct
measurement by means of fresh air. As CO
2
concentration in cultivation halls is usually much higher than outdoors, the
meter working all the time in the conditions of high concentrations of CO
2
shows a tendency to overestimate the results, what
can be prevented by periodic delivery of fresh air. This also permits verification of correct measurement – CO
2
concentration
value in external air is usually a predictable value of a few hundred ppm. A radically different result means incorrect operation
of the meter or of the entire system of collective CO
2
measurement.
The limitation in the quantity of halls taking part in the collective CO
2
measurement is duration of the measuring cycle. For
instance: at the time of air suction from the hall of 5 minutes and 5 cultivation halls plus external air measurement, we have
cycle time = 5 minutes * (5 + 1) = 30 minutes. This means updating of CO
2
result in each hall every 30 minutes. Increasing
the number of halls prolongs this time in two ways: once, that each additional hall should be considered in the cycle, two,
that the length increases of pipes supplying air to the meter and, at the same time, it may be necessary to prolong the
measurement time from one hall. Too rare updates of CO
2
concentration measurement result does not let LB-762 regulator
effective regulate fresh air supply to the hall and, at the same time, does not permit effective CO
2
level regulation.
In a greater system where the number of halls and regulators would cause too long CO
2
measurement cycle time, it is possible
to divide the collective CO
2
measurement system into smaller parts. In such case in the system a greater number is installed
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