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Defining A Data Logging Problem
Relay CH—]
BATH
BATH
HEATER
|
DISC DRIVE
[—]
CONTROLLED TEMPERATURE BATH
ROOM
LOOP 2
TEMP
LOOP 1
J
—11
1]
o|]
3 of
—
]-
00
00
HP-71
HP3421
Figure 8-1, Temperature Logging System With Actuator Control
In our example the log setup will consist of two groups: the first will will record the the room temperature
and bath temperature on the disc drive every 15 minutes; the second group will monitor and control the
bath temperature every 30 seconds.
Two limit tests are specified: the lower and upper control limits, and
the lower and upper alarm limits. The lower and upper control limits are set at 24. 5 and 25. 5°C. When
the temperature falls below 24. 5°C, the actuator channel is closed, turning on the heater by means of a
relay. When the temperature rises above 285. § °C, the actuator channel is opened, turning the heater off.
The lower and upper alarm limits are set at 24 and 26°C. If the control system fails, one of the alarm
limits will be reached and the HP-71 will beep.
The setup is designed to begin logging data an hour before a production shift starts (to bring the bath to
temperature), and to continue logging throughout the shift.
This means that group one will begin to
record data at 8:00 a.m., but group two will begin to monitor and control the bath temperature at 7:00
a.m. Group one will execute 33 times - once every 15 minutes from 8:00 am to 4:00 p.m.
Group two
will execute 1081 times - once every 30 seconds from 7:00 am to 4:00 p.m.
8-35
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