Installation manual

Output Parameters

900M050U00  Athena Controls, Inc. 7-7

7.4.3 Specify the PID Output Range

If the controlled field device should never be fully off and/or fully on, you can limit the

range of the output when PID is used. The range defined here affects both:

• the control algorithm’s output when the controller is in normal (automatic) mode, and

• the fixed output percentage the operator can enter when the controller is in manual

mode.

For example, suppose the lowest input the controlled device should receive is 30% of the

analog output’s range (or the discrete output’s cycle time), and the maximum input the

controlled device should receive is 70% of the analog output’s range (or the discrete

output’s cycle time). In this case you set the O1.LLO1.LL = 30 and the O1.HLO1.HL = 70.

• If the controller uses a 0 to 20 mA output, then the lowest output signal sent to the

field device in our example is 6 mA (30% of 20 mA), even if the process variable

requires no correction. The highest output signal sent to the controller is 14 mA

(70% of 20 mA).

• If the controller uses a normally open relay as its output, then the lowest percentage

of the cycle time the relay would be closed is 30% of the cycle time, and the highest

percentage of the cycle time the relay is closed is 70%. If the cycle time configured

with the O1.CYO1.CY parameter is 10 seconds, then the relay is never closed for less than 3

seconds (30% of 10 seconds), even if the process variable requires no correction.

The relay is never closed for more than 7 seconds (70% of 10 seconds).

The limits apply to both normal (automatic) mode and manual mode. In our example, the

operator can never turn off the field device using the controller while the output limits are

set to 30 and 70, regardless of whether the controller is in auto or manual mode.

The lower and upper output limits should not be set to the same value.

Parameter Name

: Output 1 Low Limit (A3) and Output 2 Low Limit (B4)

Name as Displayed

O1.LL O1.LL and O2.LLO2.LL

Used By:

all controllers

When Displayed:

if output type is PID

Range:

0 to 100 percent

Default:

Description:

Used to specify the lowest percentage used for the output in

both manual and normal (automatic) modes.

Effect on Other

Parameters:

No effect on other configuration parameters. However, it limits

the allowable range for the fixed output percent in manual mode.