HP VXI 75000 C Series, User'S And Scpi Programming Manual

Page: 79 / 438

Programming the HP E1415 for PID Control 79 Chapter 3
Manual control slew rate;Man_inc (defaults to 9.99E+37 (fast change))
Use the ALG:SCALAR and ALG:UPDATE commands to change the
manual control variables before or after the algorithm is running.
Status Variable
The PIDB algorithm uses 7 bits in a status variable (Status) to record the
state of clipping and alarm limits, and the automatic/manual mode. When a
limit is reached or the manual mode is set, the algorithm sets a status bit to 1.
Output (<outp_chan>) at clipping limit; Status.B0
I term (I_out) at clipping limit; Status.B1
D term (D_out) reached at limit; Status.B2
SD term (SD_out) at clipping limit; Status.B3
Control mode (Man_state) is manual; Status.B4
Error term (Error) out of limits; Status.B5
Process Variable (<inp_chan>) out of limits; Status.B6
History Mode
The PIDB algorithm provides two modes of reporting the values of its
operating variables. A variable History_mode controls the two modes. The
default history mode (History_mode = 0) places the following algorithm
values into elements of the Current Value Table (the CVT):
Process Variable (<inp_chan>) value to CVT element (10 * n) + 0
Error Term variable (Error) value to CVT element
(10 * n) + 1
Output (<outp_chan>) value to CVT element (10 * n) + 2
Status word bits 0 through 6 (Status) to CVT element (10 * n) + 3
Where n is the number of the algorithm from ’ALGn’
So ALG1 places values into CVT elements 10 through 13, ALG2 places
values in CVT elements 20 through 23 ... ALG32 places values into CVT
elements 320 through 323
When you set History_mode to 1, the operating values are sent to the CVT
as above and they are sent to the FIFO buffer as well. The algorithm writes
a header entry first. The header value is ( n * 256 ) + 4, where n is the
algorithm number from ’ALGn’, and the number 4 indicates the number of
FIFO entries that follow for this algorithm. This identifies which PIDB
algorithm the 5 element FIFO entry is from.
See the program listing for PIDB in Appendix D page 347.
Defining a PID with
ALG:DEFINE
Select the PID algorithm you want to use (PIDA or PIDB). Determine which
channels to specify for the PID input, PID output, and optionally the digital
channel to use as an alarm channel. Execute the command
ALGorithm[:EXPLicit]:DEFine ’<alg_name>’,’<alg_def_string>’.
•
<alg_name> is ALG1 for the first defined algorithm, ALG2 for the
second etc. up to the maximum of ALG32. The "ALG" is not case
sensitive. That is, ALG1, alg1, aLg1 are all equivalent.
•
<alg_def_string> contains a string that selects the PID algorithm
(PIDA... , or PIDB... ), and specifies the input, and output "channels".
PIDB also takes an alarm "channel". The general form of the string is:
PIDx(<inp_channel>,<outp_channel>,<alarm_channel>)’