RAMP (Ramp Function / Rate Limiter)
Limits rate of change to create smooth transitions between values.
The RAMP function block limits the rate of change of a signal, creating a smooth transition from one value to another at a controlled rate. Instead of allowing an output to jump instantly to a new setpoint, the ramp gradually moves the output at a maximum defined rate (units per second). RAMP is essential for motor soft-start/soft-stop, preventing thermal shock in heating systems, smooth valve positioning, and any application where sudden changes could cause mechanical stress or process upsets.
Parameters
Inputs
| Name | Type | Description |
|---|---|---|
| IN | REAL | Target value (setpoint) |
| RATE_UP | REAL | Maximum rate of increase (units/second) |
| RATE_DN | REAL | Maximum rate of decrease (units/second) |
| CYCLE | TIME | Execution cycle time |
Outputs
| Name | Type | Description |
|---|---|---|
| OUT | REAL | Ramped output value |
| BUSY | BOOL | TRUE while ramping (OUT <> IN) |
Structured Text Example
VAR
Speed_Ramp : RAMP;
Target_Speed : REAL := 1500.0; // RPM
Actual_Cmd : REAL;
END_VAR
Speed_Ramp(
IN := Target_Speed,
RATE_UP := 100.0, // 100 RPM/sec acceleration
RATE_DN := 200.0, // 200 RPM/sec deceleration
CYCLE := T#100ms
);
Actual_Cmd := Speed_Ramp.OUT;20 Production-Ready Ladder Logic Templates
Stop writing the same rungs from scratch. Get copy-paste-ready templates for motor control, PID loops, safety interlocks, conveyors, and more.
Platform-Specific Implementation
Siemens (TIA Portal)
Implement using custom FB with rate limiting logic. No built-in RAMP block.
Allen-Bradley (Studio 5000)
Use RMPS (Ramp/Soak) instruction for complex profiles, or implement custom rate limiter.
CODESYS
OSCAT library provides RAMP_REAL function block.
Common Applications
- Motor acceleration/deceleration
- Valve position ramping
- Temperature setpoint ramping
- Conveyor speed changes
- Pressure build-up control
Frequently Asked Questions
What is RAMP (Ramp Function / Rate Limiter) in PLC programming?
Limits rate of change to create smooth transitions between values. The RAMP function block limits the rate of change of a signal, creating a smooth transition from one value to another at a controlled rate. Instead of allowing an output to jump instantly to a new setpoint, the ramp gradually moves the output at a maximum defined rate (units per second).
What are common applications of RAMP (Ramp Function / Rate Limiter)?
RAMP (Ramp Function / Rate Limiter) is commonly used for: Motor acceleration/deceleration, Valve position ramping, Temperature setpoint ramping, Conveyor speed changes, Pressure build-up control.
How do I use RAMP (Ramp Function / Rate Limiter) in different PLC platforms?
Siemens: Implement using custom FB with rate limiting logic. No built-in RAMP block. Allen-Bradley: Use RMPS (Ramp/Soak) instruction for complex profiles, or implement custom rate limiter. CODESYS: OSCAT library provides RAMP_REAL function block.
Related Function Blocks
PID (Proportional-Integral-Derivative Controller)
Closed-loop feedback controller using proportional, integral, and derivative terms.
View Reference →PWM (Pulse Width Modulation)
Converts analog percentage to pulsed digital output with proportional duty cycle.
View Reference →LIMIT (Limiter / Clamp)
Clamps a value between minimum and maximum boundaries.
View Reference →Stop Writing Ladder Logic From Scratch
Get 20 production-ready ladder logic templates for $29 -- download instantly and use them on your next project today.
Instant download - 30-day money-back guarantee - Use on unlimited projects