Inputs and COVs - BCPro - LIT-12011908 - General System Information - BCPro System - 4.0

MS/TP Communications Bus for the BCPro System Technical Bulletin

Brand
BCPro
Product name
BCPro System
Document type
Technical Bulletin
Document number
LIT-12011908
Version
4.0
Revision date
2020-03-16
Language
English

The COVs for all AIs on CH-PCXs are fixed at .001. CH-PCG s immediately acknowledge all SA Bus COV reports. The goal is to have the total number of COVs on an SA Bus be fewer than 500 per minute. Use the following table to determine the total potential COVs per minute.

Note: The Update Interval (refresh rate for the user interface and CCT applications) depends on the Filter Setup, Process ID, and Time Constant attribute values in the Analog Input object. If a fast process (time constant of less than 100 seconds) receives its input from sensors located on SA Bus devices, excessive bus traffic can result.
Table 1. COV Rates: Inputs

Process ID

Time Constant (Seconds)

Update Interval (Hundredths of Seconds)

Approximate COVs Per Minute

Airflow

30

100

60

Airflow %

30

100

60

Airflow Difference

30

100

60

Bldg Static

30

100

60

Duct Static

30

100

60

Pump Diff P

30

100

60

CHWS-T Mixing

60

200

100

30

HWS-T Mixing

60

200

30

MA-T

80

200

30

CHWS-T HEX

90

300

20

HWS-T HW HEX

90

300

20

HWS-T Steam HEX

90

300

20

DA-H

200

600

10

DA-T

200

600

10

CWS-T

600

2,000

3

RA-H

900

3,000

2

ZN-H

900

3,000

2

ZN-T

900

3,000

2

ZN-T LC

900

3,000

2

ZN-H LC

900

3,000

2

For example, assume you have a Mixed Air Single Path, Variable Speed Supply fan with Volume matching system. The list of sensors includes discharge air temperature, mixed air temperature, duct static pressure, supply flow, and return flow. The following table shows how to calculate the COV rate.

Table 2. Change of Value Rate Calculation: Inputs

Sensor

Process ID

Update Interval (Hundredths of Seconds)

Approximate COVs Per Minute

Duct Static

Duct Static

100

60

Supply Flow

Airflow

100

60

Return Flow

Airflow

100

60

MA-T

MA-T

200

30

DA-T

DA-T

600

10

   

Total

220

When these sensors are located on SA Bus devices, 220 is the expected COV rate. This number is below the maximum of 500 COV, and no communication issues should result.