Ramp

Function

Shape the variation in a value over time (ratio or ramp function). The resulting ramp can have a maximum of two curves.

RAMP translates an input into a proportional output based on a set of user-defined curves.


Fig. 232.   Wire-sheet Icon

Fig. 233.   Property Sheet


Fig. 234.   Slot Sheet


Inputs and Outputs

Table 145.   Inputs

Inputs

Type

Functional description

In Ramp

numeric

Input value

In Enabled

boolean

If the input “In Enabled” is set to false disabled in the slot sheet, the output “Out” will be disabled and is set to the value “0”.


Table 146.   Outputs

Outputs

Type

Functional description

Out Ramp

numeric

Analog output signal


Parameter List

Table 147.   Parameter List

Description

Value Range

Default Value

Unit

P1 Ymin

minimum output value

-...

0

-

P2 Ymax

maximum output value

-...

100

-

P3 Xmin

minimum input value

-...

0

-

P4 Xmax

maximum input value

-...

100

-

P5 Xa

minimum input value of the first ramp

-...

0

-

P6 Ya

minimum output value of the first ramp

-...

0

-

P7 Xb

maximum input value of the first ramp

-...

50

-

P8 Xc second

minimum input value of the second ramp

-...

50

-

P9 Ybc

maximum output value of the first ramp minimum output value of the second ramp

-...

50

-

P10 Xd

maximum input value of the second ramp

-...

100

-

P11 Yd

maximum output value of the second ramp

-...

100

-


Ramp application examples

The parameters dialog box allows you to define the two curves graphically. In the following example, the first curve is selected, that is, there is an empty area within the two axes outlined by a box. This box is where the first curve appears as you define the ranges for the Ya, Yb, Xa, and Xb variables.


Fig. 235.   Ramp dialog box

Use the following procedure to create two curves for the desired “Out Ramp” output.


Relative humidity like compensated setpoint

  1. Enter the values for ramp (Ymin, Ymax, Xmin, Xmax, Xa, Xb, Xc, Xd, Ya, Ybc, Yd).
  2. Click OK to confirm your entries.


The following diagram shows how the software interprets the graph.


Fig. 236.   Ramp dialog box example 2


Scale Changes

When you change the minimum and maximum X and Y scale values, the Ramp statement adjusts the minimum and maximum values for the curves so that they are not outside the overall X and Y ranges.

For example, assume an application has the following values:

Y scale ranges from 0 through 100 (Ymin through Ymax)

X scale ranges from 0 through 100 (Xmin through Xmax)

Curve 1        X scale ranges from 20 through 40 (Xa through Xb)

       Y scale ranges from 25 through 80 (Ya through Ybc)

Curve 2        X scale ranges from 65 through 85 (Xc through Xd

       Y scale ranges from 80 through 55 (Ybc through Yd)

Fig. 237.   Ramp dialog box example 2


If you increase the minimum on the Y scale from 0 to 30, Ramp changes the Y scale minimum for Curve 1 from 25 to 30 so that the curve stays within the minimum and maximum Y scale range.


Fig. 238.   Ramp dialog box example 2 rescaling the Ymin value


If you decrease the maximum on the Y scale from 100 to 60, RAMP changes the Y scale maximum for Curve 1 from 80 to 60 (within the overall Y-scale range). Ramp also changes the Y scale minimum for Curve 2 from 80 to 60 for the same reason.


Fig. 239.   Ramp dialog box example 2 rescaling the Ymax value


Ramp Example

This example shows a room temperature setpoint with winter and summer compensation:


Fig. 240.   Compensated setpoint with Ramp connected to a PID controller


Set Ymin, Ymax, Xmin, and Xmax to determine the scale limits.


Fig. 241.   Compensated setpoint with winter and summer compensation

Winter compensation:

OAT                room temp. setpoint

Xa        -5        Ya        22

Xb        20        Ybc        20


Summer compensation:

OAT                room temp. setpoint

Xc        20        Ybc        20

Xd        25        Yd        22