FC 12 - High / Low Compare

This function has two outputs. When the input is equal to or exceeds the high limit, output N equals logic 1. When the input is equal to or less than the low limit, output N+1 equals logic 1. If the value of the input is between the assigned limits, both outputs are a logic 0.

 

NOTE: This block uses two consecutive addresses for the outputs.

 

Outputs:

Blk

Type

Description

N

B

High alarm output:

0 = high limit not reached

1 = high limit reached

N+1

B

Low alarm output:

0 = low limit not reached

1 = low limit reached

 

 

Specifications:

Spec

Tune

Default

Type

Range

Description

S1

N

5

I

Note 1

Block address of input

S2

Y

0.00

R

Full

Value of alarm point / high limit

S3

Y

0.00

R

Full

Value of alarm point / low limit

 

NOTES:

1. Maximum values are: 9,998 for the BRC-100, IMMFP11/12 and 31,998 for the HAC

 

 

 

12.1 Applications

Figure 12-1 shows function code 12 used as a signal monitor. In this example the signal shows tank level and function code 12 activates high (eight feet) and low (two feet) level alarms.

 

 

Function code 12 may also be used to indicate when the difference between two related signals is more or less than desired as shown in Figure 12-2. In this example air flow is subtracted from fuel flow by using function code 15, and function code 12 monitors the difference. If the difference exceeds a preset value, it will cause the appropriate alarm to be activated.