Campbell CR800 Series, Operator'S Manual

Page: 392 / 598

Section 8. Operation
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Tips for writing a control program:
• Short Cut programming wizard has provisions for simple on/off control.
•
PID control can be done with the CR800.
Control decisions can be based on time, an event, or a measured condition.
Example:
In the case of a cell modem, control is based on time. The modem requires 12 Vdc
power, so connect its power wire to the CR800 SW12V terminal. The following
code snip turns the modem on for ten minutes at the top of the hour using the
TimeIntoInterval() instruction embedded in an If / Then logic statement:
If TimeIntoInterval ( 0,60,Min) Then PortSet (9,1) 'Port “9” is
the SW12V Port. Turn phone on.
If TimeIntoInterval (10,60,Min) Then PortSet (9,0) 'Turn phone
off.
TimeIsBetween() returns TRUE if the CR800 real-time clock falls within the
specified range; otherwise, the function returns FALSE . Like
TimeIntoInterval() , TimeIsBetween() is often embedded in an If / Then logic
statement, as shown in the following code snip.
If TimeIsBetween (0,10,60,Min) Then
SW12 (1) 'Turn phone on.
Else
SW12 (0) 'Turn phone off.
EndIf
TimeIsBetween() returns TRUE for the entire interval specified whereas
TimeIntoInterval() returns TRUE only for the one scan that matches the interval
specified.
For example, using the preceding code snips, if the CRBasic program is sent to
the datalogger at one minute past the hour, the TimeIsBetween() instruction will
evaluate as TRUE on its first scan. The TimeIntoInterval() instruction will
evaluate as TRUE at the top of the next hour (59 minutes later).
•
Note START is inclusive and STOP is exclusive in the range of time
that will return a TRUE result. For example:
TimeIsBetween (0,10,60,Min) will return TRUE at 8:00:00.00 and
FALSE at 08:10:00.00.
8.3.1 Terminals Configured for Control
C terminals can be configured as output ports to set low (0 Vdc, turn off) or high
(5 Vdc, turn on) using the PortSet() or WriteIO() instructions. Port C4 can be
configured for pulse width modulation with a maximum period of 36.4 s. A
terminal configured for digital I/O is normally used to operate an external relay-
driver circuit because the port itself has limited drive capacity.Current sourcing
for drive capcitiy is determined by the 5 Vdc supply and a 330 Ω output
resistance. It is expressed as: