FC 179 - Enhanced Trend

The enhanced trend definition function code is part of the Symphony distributed trending package. This function code collects, compresses and stores trend data. A compression algorithm increases the amount of historical data retained by the block for a given amount of module memory utilization. Trend data may be collected from various exception reporting blocks, identified by S2.

 

Collected data can be retrieved from the block on demand by any number of collection devices for archiving and display.  The enhanced trend block issues special trend exception reports and notifies collection devices when a significant amount of new trend data is recorded in the trend buffer.

 

The amount of historical data retained by the block varies depending on:

 

Function code 179 gives the following enhancements over the analog trend function code 66:

 

 

Outputs:

Blk

Type

Description

N

R

Value is always 0. Quality is bad when the Harmony controller has not been time synchronized.

N+1

R

Approximate number of minutes of historical data currently saved in the block's buffer.

 

 

Specifications:

Spec

Tune

Default

Type

Range

Description

S1

N

0

I

Note 1

Block address of input

S2

N

0

I

0 - 9

Input block type:

0 = function code 30 or 48

1 = function code 45 or 67

2 = function code 62

3 = function code 68

4 = function code 80

5 = function code 123

6 = function code 129

7 = function code 136

8 = function code 177

9 = function code 211

10 = function code 222

11 = function code 223

12 = function code 224

13 = function code 225

14 = function code 229

S3

N

1

I

1 - 63

Trending mode:

1 = sampling         8 = average

2 = minimum       16 = sum

4 = maximum      32 = range (max.-min.)

S4

N

50

I

20 - 65535

Buffer size (no. of events)

S5

N

40.000

R

0 - 100

Buffer threshold (%)

S6

Y

15.000

R

Full

Input sampling time (secs)

S7

Y

1.000

R

0 - 100

Significant change (%)

S8

N

1200.000

R

Full

Maximum elapsed time for event recording (secs)

S9

Y

1.000

R

Full

Statistical time base period

S10

N

2

I

0 - 3

Statistical time base units:

0 = seconds         2 = hours

1 = minutes          3 = days

S11

N

7200.000

R

Full

Maximum elapsed time for exception reporting (secs)

S12

Y

100.000

R

0 - 100

GOOD / SUSPECT threshold

S13

Y

1.000

R

Full

Summation conversion divisor

S14

N

1

I

Full

Summation modifier

S15

N

0

I

Note 1

Block address of statistical time base reset signal

S16

N

0

I

Full

Spare parameter

S17

N

0

I

Full

Spare parameter

S18

N

0

I

Full

Spare parameter

S19

N

0.000

R

Full

Spare parameter

 

NOTES:

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

 

 

179.1   Explanation

 

179.1.1  Specifications

S1

(Block address of input) Block address of exception report block to be the source of trend data.

 

NOTES:

  1. When addressing a multiple output block, use the lowest block number (N).

  2. Selecting a value of zero disables all sampling and statistical trending for the function code 179 block.

 

 

S2

(Input block type) Identifies type of input to be trended.

0 = function code 30 or 48, analog exception report

1 = function code 45 or 67, digital exception report

2 = function code 62, remote control memory

3 = function code 68, remote manual set constant

4 = function code 80, control station

5 = function code 123, device driver

6 = function code 129, multi state device driver

7 = function code 136, remote motor control

8 = function code 177, data acquisition analog

9 = function code 211, data acquisition digital

10=function code 222, analog in/channel

11=function code 223, analog out/channel

12=function code 224, digital in/channel

13=function code 225, digital out/channel

14=function code 229, pulse in/channel

 

NOTE: The block addressed in <S1> must match the input block type in S2 or a configuration error will result.

 

S3

(Trending mode) Selects any combination of available trending point types. None are exclusive; any or all may be selected simultaneously.

Specification S6 selects sample collection speed, while S9 and S10 select the statistical time base period.

1 = Sampling - current value.

2 = Minimum - minimum value collected over the statistical time period (S9 and S10).

4 = Maximum - maximum value collected over the statistical time period (S9 and S10).

8 = Average - (arithmetic mean) - average value collected over the statistical time period (S9 andS10).

16 = Sum - total values collected over the statistical time period (S9 and S10).

32 = Range - value of maximum minus minimum samples collected over the trending interval(statistical).

 

Example:

 

The exception report selected is to be trended in the Sampling (one) and Range (32) modes.

1 + 32 = 33

S3 = 33

S3 = sum of desired modes

 

NOTES:

  1. When any statistical mode is selected, the statistical calculations are not cumulative from one statistical time period to the next.

  2. When sampling mode is selected, status and alarm information is recorded, as well as a value for each input block type.

 

The types of trend data available for display or analysis depends on the capabilities of the device used to collect, display, or analyze the data recorded by the enhanced trend block. Consult the user's manual for the specific device used for a description of the data available and the procedures for configuring that device. When trending a digital signal using average, trend value represents percent of time ON or OFF (duty cycle) (zero to 100 percent).

 

S4

(Buffer size) Specifies the minimum number of events that may be recorded by setting an amount of module memory aside for the trend data buffer.

 

Increasing the trend buffer size will:

 

An event is one of the following:

 

 

The maximum allowable value for S4 depends on the setting of S2.

 

 

S5

(Buffer fill threshold) The percent of buffer space filled with new events before informing collecting devices of a significant amount of new available trend data.

 

NOTE: The effect of this parameter is highly dependent upon system dynamics and should not be changed without careful analysis. Decreasing the threshold causes the collection devices to retrieve data more frequently, resulting in an increased load on the system. Increasing the threshold causes the collection devices to retrieve data less frequently and could result in lost data. It is recommended that S5 be left at the default 40% value to guarantee enough collection time to account for process upsets. In any case, S5 should not be set greater than 80%.

 

S6

(Input sampling time, in seconds; only used if sampling is selected in S3) The period of monitoring the value and status of the sampling input.

 

NOTE: Selecting a value of zero disables the sampling mode.

 

S7

(Significant change; in percent of span) Determines if the result of the statistical computations of the current period deviate by a specific percentage from the result of the previous period. The block projects an expected value by observing the trend of previous values. When the actual input value differs from this expected value by more than the specified amount, a new value is recorded. The enhanced trend block uses this value along with the span values defined in the exception reporting block that is referenced by S1 to calculate its absolute significant span values. The significant change values defined in these exception reporting blocks do not affect the enhanced trend compression algorithm.  Specification S7 also affects the compression algorithm for storage of statistical computations (minimum, maximum, sum, range, and average). However, S7 does not affect calculation of statistical values.

 

S8

(Maximum recording time) Maximum interval between consecutive recorded values in the trend buffer for one point. The maximum recording time specification insures that both sample and statistical trend values will be recorded if none have been recorded for this specific amount of time. Statistical values will not compress if this time is less than the statistical period (S9 and S10). They will be stored after the end of each statistical period. Likewise, if this time is less than the input sampling time (S6), the input sampling compression algorithm will be effectively disabled. This forces input samples to be recorded at the end of every input sample period. This is useful in applications that require data that is recorded at fixed time intervals.

 

S9

(Statistical time base period; only used if S3>1) Determines the period of the statistical computation when the trending mode in S3 is set for one of the statistical functions. The statistical time base units are set by S10. For example: If S9 equals five and S10 equals one, then the period of the statistical function set by S3 is five minutes.

 

NOTE: Use the smallest number possible (i.e., S9 = 1 and S10 = 2 for one hour rather than S9 = 3,600 and S10 = 0 which equals one hour in seconds).

 

When the period set by S9 and S10 equals one hour (S9 equals one, S10 equals two) or one day (S9 equals one, S10 equals three), the statistical computation period synchronizes to real time. The statistical function is calculated on the hour or on a daily (at midnight) basis. All other statistical periods are elapsed time and are not synchronized to real time.

 

A reset on S15 disables real time synchronization. When a reset on S15 occurs, real time synchronization is disabled and the statistical period begins on an hourly or daily basis from the time of the reset. To enable real time synchronization, tune S9 to another value then return it to a value of one (i.e., tune S9 to three, then tune S9 to one). If S9 equals zero, the statistical mode trending function is disabled.

 

S10

(Statistical time base units) Shows the time unit associated with S9.

0 = seconds

1 = minutes

2 = hours

3 = days

 

S11

(Maximum reporting time; in seconds) Maximum interval between trend exception reports. Gives an exception report if no other criteria has prompted one. This notifies collection devices to collect trend data.

 

S12

(Good/suspect threshold) Minimum percentage of input values during a statistical period that must be good quality to receive a GOOD summary value. If at least one good value is observed, but the percentage of good values is less than this parameter value, the quality of the summary will be SUSPECT. If no GOOD values are observed, the summary value will be BAD.

 

S13

(Summation conversion divisor; used only if summation is selected in S3) Value used to compute the sum over the period set by S9 and S10. Summation conversion divisor is a divisor into the accumulated sum and may be used to adjust for differences in the units of a value. Summation computation is calculated by adding the current sampled input value to the total every segment cycle time.

 

Example:

 

Target segment cycle time equals 0.25 second:

 

1 value collected every 0.25 second = 4 values added to sum every 1 second = 240 values added to sum every 1 minute

 

If the source point value is in units of gallons per minute, a conversion divisor of 240 would adjust the sum to have units of gallons.

 

NOTES:

  1. If a value of zero is selected for the summation conversion divisor, a value of 1.0 will be used instead.

  2. The target segment cycle time is set in the executive block, function code 82. A value of zero entered for the target segment cycle time disables the summation statistic.

 

For digital inputs, the sum might show the number of segment cycle times during which the input was a one. In such a case, the conversion factor might be used to convert the sum to units of run time.

 

S14

(Summation modifier; only used if sum is selected in S3, and S2 = 1, 2, 5, 6, or 7) Specifies the type of summation function for digital inputs.

 

0 = count number of samples when input was zero

1 = count number of samples when input was one

2 = count changes from zero to one

3 = count changes from one to zero

4 = count all state changes

 

S15

(Block address of statistical time base reset signal) Resets the periodic function timer based on S9 and S10 when the referenced block shows a transition of 0 to 1. The current statistical period immediately ends and a new one starts. This allows configuration control over periodic trend functions.

 

Example:

Hourly statistics for a trended point are typically configured to be synchronized to real-time (refer to S9), but may be synchronized to process events (such as an operation startup) by using this input.

 

S16 through S18

Spare integer.

 

S19

Spare real.

 

 

179.2   Applications

 

To trend analog values, the user configures the analog exception reports and enhanced trend blocks for each point trended.

 

Figure 179-2 illustrates a configuration of a sampling (once a minute) and average (once an hour) trend of an analog point with manual reset. The significant change allowance (S7) is set to a higher value than default. This will decrease the amount of recorded values. The human system interface (HSI) may then be configured to collect data from the enhanced trend block for display or archiving via special enhanced trend data poll messages and replies.

 

 

Figure 179-2 represents a sampling and average (hourly) and sum trend of a device driver. The sum trend is configured to count changes from zero to one. The enhanced trend block gathers all data from the device driver including state of control output, all feedback inputs, and other status indicators such as feedback status and status override.

 

 

 

 

The average will give the duty cycle of the device (percent of the period during which the device was ON) and the sum will show the number of times the device turned ON during the period (cycled from OFF to ON).

 

When the enhanced trend is used for sampling, minimum and maximum trending of a control station (function code 80), any or all points associated with the control station may be displayed. These points include process variable (PV), set point (SP), control output (CO), ratio index value (RI), and all station status indicators such as auto/manual, bypass, etc.

 

Figure 179-3 is a sample (every five seconds) trend of a control station with a reset from the start of a batch process. An increased buffer size (S4) allows for retention of more data.