ADAPTS (Adaptive control, single) - User Guide - PXC4.E16.A - PXC5.E24.A - PXC7.E400.A

pv

Process variable that is being controlled.

- This parameter can be a point name or local variable. It is usually an LAI point, but can be an LAO point–a calculated point representing a temperature, flow rate, air velocity, etc.

- This value should be between llpv and hlpv.

cv

Controlled variable (loop output). This signal is 0.0 to 100.0 percent, direct acting, and is intended to go to TABLE statements–one for each output actuator point (for example, heating, dampers and cooling).

-  This parameter can be a point name or local variable. It is usually an LAO point that represents an actuator signal.

sp

Setpoint for the loop against which the process variable is compared.

-   This parameter can be entered as a point name, local variable name, or decimal number.

-   This value must be between llpv and hlpv, and should represent the same engineering units as the process variable.

st

Sample time (in seconds). This is the time, in seconds, between two successive starts of execution of the ADAPTM algorithm. It is also the time interval between two samples of data by ADAPTM.

-  This parameter can be an integer, point name, or local variable name.

- The minimum sample time allowed is 1 second.

- The Sample Time must be less than or equal to one-third of the Time Constant. That is,

Where:

st is the Sample Time, and

tc is the Time Constant.

Suggested Sample Times

Temperature Loops (single input, single output)

-  5 seconds for fast loops;

- 10 seconds for slow loops.

Humidity Loops

- 5 to 10 seconds for return air or space loop;

- 1 or 2 seconds for a discharge air loop.

Flow and Static Pressure Loops

- 1 or 2 seconds

kc

Control gain.

-  This parameter can be a point name, local variable name, or decimal number.

-  This value must be greater than 0.0.

-  Since ADAPTS will adapt to the process it is controlling, set kc to 3.0 for both English and SI Unit applications.

tc

Time constant (in seconds). The Time Constant value is a rough estimate of the time constant of the process.

-  This parameter can be a point name, local variable name, or decimal number.

-  This value must be greater than or equal to 3 times the st value. Note: Increasing the value of tc slows down the adaptation process.

Cooling Coils

Use the following formula:

Where:

tc = ADAPTS cooling time constant parameter entry (in seconds).

CFMmax = Maximum or design airflow rate in cubic feet per minute.

L/s air max = Maximum or design airflow rate in liters per second.

GPMmax = Maximum or design chilled water flow rate in gallons per minute.

L/s chilled water max = Maximum or design chilled water rate in liters per second.

Tsensor = time constant of the supply air sensor; typically about 30 seconds.

Tcc actuator = stroke time of the cooling coil actuator; typically 30 seconds.

Heating Coils

Use the following formula:

Where:

tc = ADAPTS heating time constant parameter entry (in seconds).

CFMmax = Maximum or design airflow rate in cubic feet per minute.

L/s air max = Maximum or design airflow rate in liters per second.

GPMmax = Maximum or design hot water flow rate in gallons per minute.

l/s hot water max = Maximum or design hot water rate in liters per second.

Tsensor = time constant of the supply air sensor; typically about 30 seconds.

Thc actuator = stroke time of the heating coil actuator; typically 30 seconds.

Mixed Air Temperature

Use the following formula:

Where:

tc = ADAPTS mixed air temperature time constant parameter entry (in seconds); typically 40 seconds.

Tma sensor = time constant of the mixed air temperature sensor; typically about 30 seconds.

Tdamper actuator = stroke time of the mixed air damper actuator; typically 30 seconds.

Duct Static Pressure

-  6 seconds for small size systems,

-  10 seconds for medium size systems, and

-  20 seconds for large size systems.

Airflow Control

-   6 seconds for small size systems,

-  10 seconds for medium size systems, and

- 20 seconds for large size systems.

Duct Humidity Control

-  50 seconds for small size systems,

- 100 seconds for medium size systems, and

-  200 seconds for large size systems.

Cascade Control (setpoint reset)

For the return air/room air (outer/slow) temperature or humidity loop:

- 100 seconds for small size systems/rooms*,

-  250 seconds for medium size systems/rooms*, and

-  500 seconds for large size systems/rooms*.

* A full room should have a longer time constant than an empty room.

ra

Reverse acting flag. This parameter defines the action of the ADAPTS controller.

- Reverse acting means cv (output) decreases as pv (input) increases.)

- This parameter can be an integer, point name, or local variable name.

-  Valid values are 0 and 1.

1 = reverse acting

0 = direct acting

llpv

Low limit of process variable. The llpv is typically the lowest value that the pv is expected to achieve. This value may differ from the sensor’s low range.

- This parameter can be a point name, local variable name, or decimal number.

- This value must be less than hlpv.

hlpv

High limit of process variable. The hlpv is typically the highest value that the pv is expected to achieve. This value may differ from the sensor’s high range.

- This parameter can be a point name, local variable name, or decimal number.

- This value must be greater than llpv.

llcv

Low limit of control variable. The llcv represents the low limit of the ADAPTS output.

- This parameter can be a point name, local variable name, or decimal number.

- This value must be less than hlcv.

- For electric actuators, typically llcv is 0.0% or 0.0 volts.

- For pneumatic actuators, typically llcv is the low end of the actuator spring range.

hlcv

High limit of control variable. The hlcv represents the high limit of the ADAPTS output.

- This parameter can be a point name, local variable name, or decimal number.

- This value must be greater than llcv.

- For electric actuators, typically hlcv is 100.0% or 10.0 volts.

- For pneumatic actuators, typically hlcv is the high end of the actuator spring range.

edb

Error deadband. This parameter determines how much error (process variable minus setpoint) must exist before ADAPTS recalculates its output signal (control variable).

Noisy process variable signals can cause much actuator movement. Setting edb to a value equal to that of the noise will eliminate unnecessary actuator movement. Thus, actuator repositioning, and actuator life, can be affected by the use of this parameter.

- This parameter can be a point name, local variable name, or decimal number.

- This value must be greater than or equal to 0.0.

- The drawback when setting edb to a non-zero value is lack of control accuracy when near setpoint. The effective setpoint becomes the value of parameter sp +/- edb.

- Initially set edb to the loop’s maximum allowable setpoint tolerance.

         - For temperature and humidity loops, edb can be very low–even 0.0 is acceptable.

         - For static pressure and flow loops, start with 1% to 3% of the maximum input value.

- If small actuator oscillations are observed, edb can be increased in value until the maximum setpoint tolerance is reached.

npv

Noisy process variable. Noisy means that the value of the process variable jumps up or down abruptly from one sensor scan to another.

Some processes inherently create a noisy process variable signal. An airflow signal, for example, can be very noisy at the low end of its sensor range due to a lack of resolution. Other processes can be noisy under certain conditions. For example, a static pressure signal can be noisy at certain fan speeds and with a certain sensor positioned too close to the fan.

- This parameter can be an integer, point name, or local variable name.

- In general, follow these rules:

        -  npv = 1 (noisy) for a loop with a very noisy pv, such as airflow or static pressure control. Adaptation is slowed with npv = 1.

         - npv = 0 (not noisy) for a loop with a pv that is not noisy or only a little noisy, such as temperature control or humidity control.

err

Error reporting point. ADAPTS writes to this point.

- This parameter is entered as a point name or local variable name.

- A zero indicates no error.

- A non-zero indicates an error.