Using master and slave blocks with extra signal ports

The two examples in this chapter have used the simplest master and slave blocks. The information transferred between the master and slave has been:

• hydraulic variables (pressure and flow rate)

• discrete line information

Included in the discrete line information is the time of the end of the discrete line step. This is not a constant increment and the increment will vary according to the current speed of sound in the fluid. It is treated as a discontinuity point.

Using the master and slave blocks with extra signal ports allows you to pass addition information between the master system and slave system. A signal can be sent from the slave system and it will be received as a discrete signal in the master system. The slave system will sample the master system at specific times and the signal in the slave will be constant between these times. Signals can be sent in the opposite direction in the same way. Signal information is exchanged at a constant rate defined in the slave blocks by the parameter sample interval for signal ports. This is also treated as a discontinuity point. The signal port discontinuities and discrete line discontinuities are totally independent.

This signal information can be used in a number of ways:

• Variables in a slave can be sampled by the master and used for design exploration.

• A controller can be included in the master. It can send signals to one or more slaves and can sample values in one or more slaves.

• It allows limited slave-to-slave communication with the signal routed through the master.

In the following slave system (figure Figure 29), we have a three cylinder hydraulic pump. The pressure in each cylinder is conveyed to the master block as a signal. This means the master system is able to sample these pressures. Note that in this case information from the master to the slave is of no interest, so the three ports on the master block are 'plugged'.

Figure 29: Three cylinder hydraulic pump

There are a lot of ports on these icons and care must be taken with connections. Remember that a given port number of the slave block corresponds to the same port number on the master block.

Note

A discrete partitioning run with signal port icons will be slower than one without.