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These devlces typlcally do not accept or produce ±lO V, linear slgnals. Thus,
while the system was in the PSL, the scaling for the control inputs from the
ClM unit to the engine slmulator had to be mapped to the equivalent scaling for
the hybrid slmulation. Likewlse, the scaling for the outputs of the slmulator's
sensors had to be mapped to the equivalent scaling values for the actual engine
sensors so the ClM unit received the same values the engine sensors would
produce. For some variables the difference between the hybrid and the PSL mode
was simply a different scale factor. In the nonlinear cases the PSL varlable
had to be mappedthough a look-up table or a polynomial curve in addition to
being scaled. These curves and polynomials were determined experimentally during
the englne test calibration procedure.
Calibration. - The calibration mode is used to test the input/output variable
mappings. Once a map has been determined and implemented, it must be validated
with the simulation and controller. The calibration mode allows the
user to bypass the system evolution subroutlnes, independently set a variable
to an intermediate value in engineering units, and examine the corresponding
output value. In the same way, the simulator can receive analog inputs and
the user can examine these values in engineering units once they have gone
through conversion. Using this method, the user can determine if the values
are being scaled correctly.
Closed loop/open loop. - In the closed-loop mode the simulator receives
the control signals from an outside source such as the ClM unit. In the openloop
mode the simulator uses base point values stored in its memory for the
control slgnals.
Actuator. - The actuator mode is used to simulate only the engine actuators.
To ensure that the real actuators are all working correctly and since
they are quite simple to model accurately, the simulator can be run in parallel
with the engine and the simulated and actual actuator feedback values compared.
The only difference between the actuator mode and the run mode of the simulator
is that in the actuator mode TT2, the only independent variable which the actuators
require beside the control signals, is obtained as input from the facllity
(Propulsion Systems Laboratory) rather than calculated by the simulator.
Since no other information Is required and the actuator calculations are fairly
simple and accurate, the simulator is used as a full envelope real-time slmulator
for the actuators. The engine model outputs are not used in this mode
since the base points are not recalculated at each operating point.
The modes are all defined by software switches which can be toggled using
MINDS (ref. 13). MINDS is a program used to examine and to set values of memory
locations. To the user, MINDS looks like an interpreter. The user types
in commands and MINDS carries them out. MINDS executes in the background and
is interrupted by the timer at the beginnlng of each initialization or run-tlme
cycle (fig. 6). Even though it runs for only about 17 percent of the time in
the run-tlme loop, to the user it appears to be running cont!nuously. MINDS
can be used to examlne and/or set the software mode switches and also to
examine and set any parameter within the simulation. In addition, MINDS can
be used to collect transient data, that is, to examine memory locations periodically
over time, and to display that information graphically. Due to memory
constraints in the simulator, the transient data capability of MINDS was not
Included.
The simulator uses the CP/M-86 disk operating system for loading the simulator
program from disk, for saving MINDS data to disk, and for communicating
with the user terminal. This operating system has a limitation that the total
space for code and data may not be more than 64 Kb. The total memory required
for the simulator, including the reduced capability version of MINDS, is about
50 Kb, approxlmately two-thirds of which is code and one-third is data.
PROGRAM EXECUTION
After the system is booted, the program can be executed by typing the name
of the disk drive where the program disk is located followed by a colon and the
name of the program. When the RETURN key is pressed, the executable code is
loaded from disk and executed.
The program starts execution in the executive (fig. 7). The executive
initializes the update intervals, sets up the memory appropriately and takes
care of the administrative details. Then it executes two routines, MSET
(fig. 8) and MTRXST (fig. 9). They are routines for initialization of constants
such as time constants, the exponents associated with each time constant,
and the initial conditions. Once the program setup is complete it is
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