UDG1606 Process Instrumentation & ControlFaculty of Chemical & Natural Resources Engineering

CHAPTER 8Presentation of Data

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Introduction

• The presentation of data…

▫ …the translation of process variables into a format that conveniently displays (for human or presents for machines)

▫ ……the changes of the process variables with time.

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Introduction

• The purpose of data presentation is to…

– … provide a human or a machine with values of related process variables over a period of time

– …….so that the status and trend of the process can be can be monitored or changed continuously.

• From the presentation display, human can

- monitor 3 mains signals (set point, sensor feedback and controller output)

- change set point and controller output

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Controller

Final Control element

Process

e = r - b

r

b

p

u

c

Measurement

Transmitter

3 major signals are presented to humans which are the set point (r), the measurement signal (b) and controller

output (p). But human can only change the set point and controller output

Pressure Gauge

• Simplest presentation of data → human operator.

• The pressure of the entered fluid of process and drives the indicator correspondingly.

• So it may have problems of safety (process material hazard), mounting (top but read on the ground → error), and location (hard to read – parallax).

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Pressure Gauge

• Reader has to record the measurement at the local area even though it’s simpler and less expensive.

• The pressure gauge presents valuable data to a human operator, but it does not achieve the capability required in most current applications.

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Multipoint Strip Chart Recorder

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Multipoint Strip Chart Recorder

▫ Format – in this case trend curves of dots drawn by a pen on a paper graph for process variables A and B.

▫ Accuracy – depends on pen calibration and resolution plus the calibration of the sensors and the shielding of the transmission medium from interference.

▫ Timing – the vertical coordinate shows the time when each dot occurred in hours and minutes.

▫ Frequency – time between the dots.

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Data Acquisition System

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Honeywell TDC 3000

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Overview Display

• Operator can view or monitor the status of overall process

• This “big picture” shows the status of up to 36 groups, with each group having up to eight variables, for a maximum of 288 variables

• Each group is identified with a tag number and a short title.

• Set point ~ horizontal line with a space separating each group.

• If there is deviation, it will show whether lower (vertical line below) or upper (vertical line above) than the set point (from the set point line).

• Position of each variable is noted as M = manual mode, F = hardware failure, ? = communication error, and A= alarm.

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Overview Display

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If any of variables in the group deviate from set point, a vertical line below or above the set point will

appear

Group Display

• For any group point on the group display, the operator can change:-

– Set point value

– Control mode (manual, auto, or cascade)

– Controller output value when in manual mode.

• He does this by selecting one of the eight points on the group display using one of eight buttons. Then X will display.

• Then he may use the special set point buttons to enter desired numerical value or to increase or decrease the set point The output value will then changed automatically and gradually.

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Group Display

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This group shows 7

analog variables

and 1 digital variable

Selected point to be changed

by the operator,

either setpointchanges or

output changes

Yokogawa Group Display

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Honeywell TDC3000 Group Display

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Point Display

• The detail associated with one process variable is exemplified on the point display.

• The information on the group display is duplicated for the variable in the point display with controller tuning constants, alarm setting, and the loop hardware configuration, plus other parameters.

• To the right are values entered by the control engineer for the loop controller tuning constants and range. These include:-

– Gain, K = 0.1-100

– Integral time, T1 = 0.02-91 minutes/repeat

– PV (process variable) filter time constant = 0.0006-17 minutes

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• Further to the right on the figure are constraint settings for the output signal, integral action, and settings for process variable HI and LO alarms and for the overview alarms.

• The operator may change the set point, the control mode, and the output from this display in the same way as the operator changes them from the group display.

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Point Display

Trend display

• The trend display can be selected for 60 averages each of 20 seconds duration, or 1 minute, 3 minutes, 6 minutes, or 12 minutes. As each new average come in and updates the display at the right, the oldest bar disappears from the left.

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Trend Display

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Yokogawa Trend Display

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Honeywell TDC3000 Trend Display

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Hourly average display

• The hourly average display replaces the bar graphs on the group display with 10 hours of averaged numerical values to form a shift report for the group that may be printed on the printer as well as shown on the display.

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Hourly Average Display

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Alarm Summary Display

• The alarm summary display is a special grouping of up to 100 alarm points.

• 20 points per page, showing high, low, and deviation status with tag and process description with information on weather the alarm is flashing (not yet acknowledged by the operator), disabled, or steady (acknowledge, but still in alarm).

• When the point returns to a normal value, the alarm is simply removed from the display if it has been acknowledged.

• If more than 100 alarms have not been acknowledged or have not return to normal, then the message “ EXCESS ALARMS” appears next to the number of active alarms, and the oldest alarms are dropped from the list, so that only 100 alarms remain in the list. 27

Alarm Summary Display

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