Simulink-PS Converter

Convert Simulink input signal into physical signal

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Utilities

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Description

The Simulink-PS Converter block converts the input Simulink^® signal into a physical signal. Use this block to connect Simulink sources or other Simulink blocks to the inputs of a Physical Network diagram.

To convey signal conversion while taking up minimal canvas space, the block icon changes dynamically based on whether it is connected to other blocks.

When Block Is...	Block Icon
Unconnected
Connected to other blocks

The block icon also changes based on the value of the Input filtering order parameter, to indicate whether filtering is being applied to the input signal.

Input Filtering Order	Unconnected Block Icon	Connected Block Icon
First-order filtering
Second-order filtering

You specify the desired unit as the Input signal unit parameter. The parameter value controls the unit of the physical signal at the output port of the block, which serves as the input signal for the Simscape™ physical network.

Note

You can also specify a physical unit on the Simulink signal connected to the input port of the block. In this case, the software checks that the two units match (for more information, see Working with Simulink Units). The Simulink signal units do not propagate into the physical network.

If you leave the block unitless, with the Input signal unit parameter set to 1, then the physical signal unit is inferred from the destination block. The default destination block units are meter-kilogram-second or MKS (SI). If you specify different units, commensurate with the expected default units of the destination block input, then the unit manager attaches these units to the input Simulink signal value and performs the necessary unit conversion when providing the signal to the destination block.

In the diagram below, the Ideal Torque Source block expects a torque signal, in N*m, on its S port. The Constant source block provides the value for this input signal. If you left the Simulink-PS Converter block unitless, the Ideal Torque Source block would generate torque of 1000 N*m. The parameters of other blocks in this example are chosen so that the output value of the Ideal Torque Sensor block is equal to the torque generated by the Ideal Torque Source block, and therefore the Display block would show the value of 1000. If you change the Input signal unit parameter value in the Simulink-PS Converter block to N*cm, the unit manager performs the conversion and the Ideal Torque Source block generates torque of 10 N*m; the torque value in the Display block changes to 10, as shown in the diagram.

When the input signal is related to thermodynamic variables and contains units of temperature, you must decide whether affine conversion needs to be applied. For more information, see When to Apply Affine Conversion. Usually, if the input signal represents a relative temperature, that is, a change in temperature, you need to apply linear conversion, ΔT_new = L * ΔT_old (the default method). However, if the input signal represents an absolute temperature, you need to apply affine conversion, T_new = L * T_old + O.

For example, in the Simulink-PS Converter block shown in the following diagram, if you type degC in the Input signal unit field and select the Apply affine conversion check box, the temperature generated by the Ideal Temperature Source block is equal to 293.15 K. However, if you leave the Apply affine conversion check box clear, the output of the Ideal Temperature Source block is 20 K.

Note

Untyped inputs do not support affine units. If you specify affine units in a Simulink-PS Converter block and then connect it directly to an untyped input port, the signal value is converted to the corresponding fundamental unit and further mathematical operations are performed with that value.

Parameters

• Units

• Input Handling

Units

Input signal unit

Units to be assigned to the physical signal. These units must be commensurate with the expected default units of the destination block input. You can select a unit from the drop-down list, or type the desired unit name, such as rpm, or a valid expression, such as rad/s. For more information and a list of unit abbreviations, see How to Specify Units in Block Dialogs and Unit Definitions. The default value is 1, which means that the units of the physical signal at the block output match the expected default units of the destination block input.

Apply affine conversion

This check box is applicable only for units that can be converted either with or without an affine offset, such as thermal units. For more information, see Thermal Unit Conversions.

Input Handling

Filtering and derivatives

This parameter lets you decide whether to filter input and thus provide time derivatives of the input signal, or provide the time derivatives through additional input ports on the Simulink-PS Converter block:

• Provide signals — Select whether you want to provide just the input signal, or also provide time derivatives of the input signal as additional input signals, by using the Provided signals parameter. The default input handling options are Provide signals and Input only. If you use an explicit solver, it is recommended that you provide input derivatives by selecting one of the other options. For more information, see Filtering Input Signals and Providing Time Derivatives.

• Filter input, derivatives calculated — Filter the input through a low-pass filter, which also provides input derivatives. In this case, the input signal is modified (through filtering) before being converted to a physical signal. The first-order filter provides one derivative, while the second-order filter provides the first and second derivatives. If you use this option, set the appropriate Input filtering time constant parameter value, as described below.

• Zero derivatives (piecewise constant) — If your input signal is piecewise constant (such as step), this option lets you explicitly set the input derivatives to zero.

Provided signals

This parameter is applicable only if the Filtering and derivatives parameter is set to Provide signals. It lets you provide time derivatives of the input signal as additional input signals:

• Input only — Provide just the input signal. This is the default. If you select this option, the block has one Simulink input port and one physical signal output port.

• Input and first derivative — If you select this option, an additional Simulink input port appears on the Simulink-PS Converter block, to let you connect the signal providing input derivative.

• Input and first two derivatives — If you select this option, two additional Simulink input ports appear on the Simulink-PS Converter block, to let you connect the signals providing input derivatives.

Input filtering order

This parameter is applicable only if the Filtering and derivatives parameter is set to Filter input, derivatives calculated. It lets you specify the number of time derivatives computed for the input signal by selecting the filter order:

• First-order filtering — Provides only the first derivative.

• Second-order filtering — Provides the first and second derivatives.

Input filtering time constant (in seconds)

This parameter is applicable only if the Filtering and derivatives parameter is set to Filter input, derivatives calculated. It specifies the filter time constant, which controls the filtering of the input signal. The filtered input follows the true input but is smoothed, with a lag on the order of the time constant chosen. You should set the time constant to a value no larger than the smallest time interval of interest in the system. The trade-off in choosing a very small time constant is that the filtered input signal will be closer to the true input signal, at the cost of increasing the stiffness of the system and slowing down the simulation. The default value is .001 s.

 Restricted Parameters

When your model is in Restricted editing mode, you cannot modify any of the block parameters, with the following exception: if the Filtering and derivatives parameter is set to Filter input, derivatives calculated prior to entering Restricted mode, you can change the value of the Input filtering time constant parameter.

Ports

The block has one, two, or three Simulink input ports (depending on the Provided signals parameter value), located on its left side, and a physical signal output port, located on its right side (in the block default orientation).