This section is slated for expansion. Below are a few tips.
• Short Cut programming wizard has provisions for simple on/off control.
• PID control can be done with the CR1000. Ask a Campbell Scientific
application engineer for more information.
• When controlling a PID algorithm, a delay between processing (algorithm
input) and the control (algorithm output) is not usually desirable. A delay
will not occur in either sequential mode
(p. 527) or pipeline mode (p. 523),
assuming an appropriately fast scan interval is programmed, and the program
is not skipping scans. In sequential mode, if some task occurs that pushes
processing time outside the scan interval, skipped scans will occur and the
PID control may fail. In pipeline mode, with an appropriately sized scan
buffer, no skipped scans will occur. However, the PID control may fail as the
processing instructions work through the scan buffer.
• To avoid these potential problems, bracket the processing instructions in the
CRBasic program with ProcHiPri and EndProcHiPri. Processing
instructions between these instructions are given the same high priority as
measurement instructions and do not slip into the scan buffer if processing
time is increased. ProcHiPri and EndProcHiPri may not be selectable in
CRBasic Editor. You can type them in anyway, and the compiler will
recognize them.
7.9.17 Serial I/O: Capturing Serial Data
The CR1000 communicates with smart sensors that deliver measurement data
through serial data protocols.
Read More See Telecommunications and Data Retrieval
(p. 391) for background
on CR1000 serial communications.
7.9.17.1 Introduction
Serial denotes transmission of bits (1s and 0s) sequentially, or "serially." A byte
is a packet of sequential bits. RS-232 and TTL standards use bytes containing
eight bits each. Consider an instrument that transmits the byte "11001010" to the
CR1000. The instrument does this by translating "11001010" into a series of
higher and lower voltages, which it transmits to the CR1000. The CR1000
receives and reconstructs these voltage levels as "11001010." Because an RS-232
or TTL standard is adhered to by both the instrument and the CR1000, the byte
successfully passes between them.
If the byte is displayed on a terminal as it was received, it will appear as an ASCII
/ ANSI character or control code. Table ASCII / ANSI Equivalents
(p. 245) shows a
sample of ASCII / ANSI character and code equivalents.
Table 41. ASCII / ANSI Equivalents
Byte
Received
ASCII
Character
Displayed
Decimal
ASCII
Code
Hex
ASCII
Code
00110010 2 50 32
1100010 b 98 62
00101011 + 43 2b
245
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