Hold

Hold the clocked, Real input signal and provide it as continuous-time output signal (zero order hold)

Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

This block holds the clocked Real input signal u with a zero order hold and provides it as continuous-time output signal y. The clock of the input signal is inferred (that is, it needs to be defined somewhere else in the clocked partition).

To be more precise: The input signal u(ti) must be a clocked signal. The output signal y(t) is a piecewise constant continuous-time signal. When the clock of u ticks at time ti, the block output y(ti) = u(ti). Otherwise y(t), t ≥ti, is the value of u(ti) from the last clock activation at time ti. Before the first clock activation of u, the block outputs the value of parameter y_start. The value of this parameter is displayed below the icon.

Example

The following example samples a sine signal with a periodic clock of 20 ms period and delays it for 2 sample periods. The resulting signal is hold with the Hold block. As a result, the clock of hold.u starts ticking at 40 ms. The output hold.y of the block is a continuous-time signal that is present from the start of the simulation. Before the first tick of the clock of hold.u, it is set to -1.0 (= the value of parameter hold.y_start).

Hold_Model.png     Hold_Result.png
model simulation result
 

Parameters (1)

y_start

Value: 0.0

Type: Real

Description: Value of output y before the first tick of the clock associated to input u

Connectors (2)

u

Type: RealInput

Description: Connector of clocked, Real input signal

y

Type: RealOutput

Description: Connector of continuous-time, Real output signal

Used in Examples (11)

ClockedWithDiscreteTextbookController

Modelica.Clocked.Examples.SimpleControlledDrive

Simple controlled drive with discrete textbook controller (period is not used in the controller)

ClockedWithDiscreteController

Modelica.Clocked.Examples.SimpleControlledDrive

Simple controlled drive with discrete controller (period is used in the controller)

ExactlyClockedWithDiscreteController

Modelica.Clocked.Examples.SimpleControlledDrive

Simple controlled drive with discrete controller and exact periodic clocks (period is used in the controller)

ClockedWithDiscretizedContinuousController

Modelica.Clocked.Examples.SimpleControlledDrive

Simple controlled drive with discretized continuous-time controller

SubClocked

Modelica.Clocked.Examples.CascadeControlledDrive

Drive with clocked cascade controller where clocks are defined with sub-sampling and partitions with super-sampling

SuperSampled

Modelica.Clocked.Examples.CascadeControlledDrive

Drive with clocked cascade controller where fastest partition is defined with a clock and slower partition is defined with super-sampling

AbsoluteClocks

Modelica.Clocked.Examples.CascadeControlledDrive

Drive with clocked cascade controller where all partitions are defined with exact (integer) clock that need to be compatible to each other

ControlledMixingUnit

Modelica.Clocked.Examples.Systems

Simple example of a mixing unit where a (discretized) nonlinear inverse plant model is used as feedforward controller

EngineThrottleControl

Modelica.Clocked.Examples.Systems

Closed-loop throttle control synchronized to the crankshaft angle of an internal combustion engine

Sample3

Modelica.Clocked.Examples.Elementary.RealSignals

Example of a Sample block for Real signals with direct feed-through in the continuous-time and the clocked partition

Hold

Modelica.Clocked.Examples.Elementary.RealSignals

Example of a Hold block for Real signals

Used in Components (4)

CylinderAirCharge

Modelica.Clocked.Examples.Systems.Utilities.ComponentsThrottleControl

Integrates the air mass flow into a cylinder. After the charge for one cylinder is complete, resets the mass to 0.

InductionToPowerDelay

Modelica.Clocked.Examples.Systems.Utilities.ComponentsThrottleControl

Accounts for the induction-to-power stroke lag.

RotationalClock

Modelica.Clocked.ClockSignals.Clocks.Rotational

Event clock generating a clock tick each time an observed input angle changed for a rotational-interval given as variable input

HoldWithDAeffects

Modelica.Clocked.RealSignals.Sampler

Hold with (simulated) Digital-Analog converter effects and computational delay