# Downtime

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## General Description

This model is used in Dynamic Simulation only.

The Downtime unit operation can be used to calculate when downtime will occur due to Major or Minor Maintenance or because of Major or Minor Failure. Basically, the model runs a number of timers, each set up for the different events. The timers will be incremented and reset based on rules for each of the Downtime events.

The model can then set a single tag to an Active or Inactive value, depending on whether the unit is active or inactive due to maintenance or failure.

The user may also enter a different tag to be tested and, if below a defined threshold, the Minor Maintenance and Major and Minor Failure timers will be paused, or remain static. The Major Maintenance timer will continue to increment.

### Diagram

The diagram shows the default drawing of the Downtime controller.

## Inputs and Outputs

There are no connections to this unit.

## Model Theory

The Probability Density functions used for the times between major and minor failures and the times to complete the repairs are as follows:

1. Flat - Probability Density Function (P(t)):
P(t) = 0 if t < Tavg - dev or t > Tavg + dev
$P(t) = \frac{1}{2*dev}$ if Tavg - dev <= t <= Tavg + dev
2. Gaussian - Probability Density Function (P(t)):
$P(t) = \frac{1}{\sqrt{dev}}*e^{\frac{-(t-Tavg)^2}{2*dev}}$
3. Exponential - Probability Density Function (P(t)):
$P(t) = \frac{1}{Tavg}*e^{\frac{t}{Tavg}}$ (note: deviation is not used in this model)
4. None: The time to failure/repair will be exactly equal to the specified time.

## State Diagram

The Downtime unit is basically a set of Timers. These timers are incremented by the solver step time, dT, according to a number of rules. When the value of a Timer is equal to or greater than the user defined period (either Active, Inactive or Repair) then the Downtime unit will change State.

This is displayed in the diagram below:

The Table below shows the actions carried out while the unit is in each state:

## Data Sections

The default sections and variable names are described in detail in the following tables. The default Downtime access window consists of 3 sections. This number may increase or decrease, based on user configuration.

### Summary of Data Sections

1. Downtime tab - Contains general information relating to the unit.
2. T1 - The second section contains information about the first downtime event. If the user specifies more than a single downtime event, then there will be additional tabs: T2, T3, etc.
3. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.

### Downtime Page

Unit Type: Downtime - The first tab page in the access window will have this name.

Tag / Symbol

Input / Calc

Description/Calculated Variables / Options

### Requirements

On Tick box Switch the unit on (ticked) or off (cleared).
Set Tag Always Tick box If not ticked, the model will only set the output tag for first iteration and when the value changes. Therefore if the user or another controller changes the same tag it will not be overwritten by this model until the next event occurs. If ticked the model will set the output tag every iteration.
Count Input The number of independent downtime blocks required. This may be any number from 0 up to 20. The user may only change this number when the model is stopped. The unit will always add new downtime blocks after existing ones, and it will delete them starting from the last block. E.g. if you have 5 downtime blocks set up and you change this to 4, downtime block number 5 will be deleted.
Total Time Output The total time that the Downtime unit has been active. This is usually = the run time of the project.
Reset_All Button This will reset the results values and restart any offsets.
Major and Minor Maintenance options
Integral Period Tick box This relates to the active period of the unit between downtime due to maintenance. If this box is ticked, then SysCAD may adjust the active period entered to suit the step size of the project. For example, if the step size = 1 hour, and the period given is not an exact number of hours, then SysCAD will adjust this number to make it an exact number of hours. If this box is left clear, then SysCAD will use the exact number entered. This may lead to some unevenness in the periods but the total amount of active time will be correct over a long period of time.
Integral Inactive Period Tick box This is the same as IntegralPeriod except it relates to the inactive period of the unit due to maintenance. If this box is ticked, then SysCAD may adjust the inactive period entered to suit the step size of the project. If this box is left clear, then SysCAD will use the exact number entered. This may lead to some unevenness in the periods but the total amount of inactive time will be correct over a long period of time.
Action during Major Maintenance
Continue Minor Maintenance Tick box If this is enabled, then Minor maintenance will occur during Major maintenance, if the 2 periods overlap. Otherwise, the Minor maintenance timer will 'freeze' during Major maintenance, and once the Major maintenance is complete, then the Minor maintenance will be re-started.
Continue Repair Tick box If this is enabled, then any repairs due to failures will be carried out during Major maintenance, if the 2 periods overlap. Otherwise, the Failure repair timer will 'freeze' during Major maintenance, and once the Major maintenance is complete, then the repairs will be re-started.

### Individual Downtime Blocks (T1, etc)

Each independent downtime block has the following layout. Each block will be on a separate tab page.

Symbol / Tag Input / Calc Description/Calculated Variables / Options
Requirements...
Description / Desc Input Optional downtime block description.
MajorMaintenance.On Tickbox Include Major Maintenance events.
MinorMaintenance.On Tickbox Include Minor Maintenance events.
MajorFailure.On Tickbox Include Major Failure events.
MinorFailure.On Tickbox Include Minor Failure events.

#### Major Maintenance

This section is visible IF the user has ticked 'Major Maintenance On'

Required Period / RqdPeriod Input The required period, or total time period from the start of one downtime for major maintenance to the start of the next downtime for major maintenance.
Offset Input The time period before the first downtime for major maintenance will occur. This time is reset if the reset button is pressed.
Rqd Inactive Period Input The time period of the downtime for major maintenance, i.e. the period during which the equipment is inactive.
Period Display Major Maintenance Period - The time period from the start of one downtime for major maintenance to the start of the next downtime for major maintenance. This may be slightly different to the number entered if the Integral Period option has been selected.
Inactive Period Display Major Maintenance Inactive Period - The time period of the downtime for major maintenance, ie. how long the equipment is inactive. This may be slightly different to the number entered if the Integral Inactive Period option has been selected.
Count Display The number of Major Maintenance events that have occurred during the current simulation.
Remaining Time Calc The time remaining before the next Major Maintenance event.

#### Minor Maintenance

This section is visible IF the user has ticked 'Minor Maintenance On'

DoWhenMajorMaint Tickbox Tick this box to allow minor maintenance to happen during the Major maintenance period.
DoWhenMajorFailure Tickbox Tick this box to allow minor maintenance to happen during the Major Failure.
Required Period / RqdPeriod Input Minor Maintenance Required Period - The total time period from the start of one downtime for minor maintenance to the start of the next downtime for minor maintenance.
Offset Input Minor Maintenance Offset - The time period before the first downtime for minor maintenance will occur. This time is reset if the reset button is pressed.
Rqd Inactive Period Input Minor Maintenance Required Inactive Period - The time period of the downtime for minor maintenance, ie. how long the equipment is inactive.
Period Display Minor Maintenance Period - The time period from the start of one downtime for minor maintenance to the start of the next downtime for minor maintenance.
Inactive Period Display Minor Maintenance - The time period of the downtime for minor maintenance, i.e. how long the equipment is inactive.
Count Display The number of Minor Maintenance events that have occurred during the current simulation.
Remaining Time Calc The time remaining before the next Minor Maintenance event.

#### Major Failure

This section is visible IF the user has ticked 'Major Failure On'

Uptime PDF Flat The Probability Density Function (P(t)) used for time between Major Failures is a flat distribution.
Gaussian The Probability Density Function (P(t)) for time between Major Failures is a gaussian (or normal) function.
Exponential The Probability Density Function (P(t)) for time between Major Failures is an exponential function.
None The user specifies the time between Major Failures.
Uptime Average Input The average time that the equipment runs without a major failure.
Uptime Deviation Input The deviation from the average time that the equipment runs without a major failure. This is only used if a flat or gaussian Probability Density Function (PDF) is chosen.
Uptime Offset Input The amount of time that the first time to failure is reduced. This takes account of equipment which has already been running and is due for failure sooner than the Uptime Average.
Downtime PDF Flat The Probability Density Function for time to repair equipment after a Major Failure is a flat distribution
Gaussian The Probability Density Function for time to repair equipment after a Major Failure is a gaussian (or normal) function
Exponential The Probability Density Function for time to repair equipment after a Major Failure is an exponential function
None The user specifies the time to repair after a Major Failure.
Downtime Average Input The average time that the equipment is inactive due to a major failure.
Downtime Deviation Input The deviation from the average time that the equipment is inactive due to a major failure. This is only used if a flat or gaussian Probability Density Function (PDF) is chosen.
Count Display The number of Major Failure events that have occurred during the current simulation.
Time To Failure Calc The time remaining before the next Major Failure event.
Time To Repair Calc The time remaining to complete the repairs to the unit after a Major Failure event.

#### Minor Failure

This section is visible IF the user has ticked 'Minor Failure On'

DoWhenMajorMaint Tickbox Tick this box to allow minor Failure to happen during the Major maintenance period.
DoWhenMajorFailure Tickbox Tick this box to allow minor Failure to happen during the Major Failure.
Uptime PDF Flat The Probability Density Function for time between Minor Failures is a flat distribution
Gaussian The Probability Density Function for time between Minor Failures is a gaussian (or normal) function
Exponential The Probability Density Function for time between Minor Failures is an exponential function
None The user specifies the time between Minor Failures.
Uptime Average Input The average time that the equipment runs without a minor failure.
Uptime Deviation Input The deviation from the average time that the equipment runs without a minor failure. This is only used if a flat or gaussian Probability Density Function (PDF) is chosen.
Uptime Offset Input The amount of time that the first time to failure is reduced. This takes account of equipment which has already been running and is due for failure sooner than the Uptime Average.
Downtime PDF Flat The Probability Density Function for time to repair equipment after a Minor Failure is a flat distribution
Gaussian The Probability Density Function for time to repair equipment after a Minor Failure is a gaussian (or normal) function
Exponential The Probability Density Function for time to repair equipment after a Minor Failure is an exponential function
None The user specifies the time to repair after a Minor Failure.
Downtime Average Input The average time that the equipment is inactive due to a minor failure.
Downtime Deviation Input The deviation from the average time that the equipment is inactive due to a minor failure. This is only used if a flat or gaussian Probability Density Function (PDF) is chosen.
Count Display The number of Minor Failure events that have occurred during the current simulation.
Time To Failure Calc The time remaining before the next Minor Failure event.
Time To Repair Calc The time remaining to complete the repairs to the unit after a Minor Failure event.

#### Requirements

ActiveValueToSet / ActiveVal Input The value to set tag to (see below) when equipment is active (ie. not stopped due to maintenance or failure). This input is optional.
InactiveValueToSet / InactiveVal Input The value to set tag to (see below) when equipment is inactive due to maintenance or failure. This input is optional.
Tag To Set Input The tag to be set to different values (as defined above) when the equipment is active or inactive. This input is optional. An example would be the flowrate on a feeder or the flow in a splitter.
Use Test tag Tickbox If this is enabled then the user may select a Test Tag, as described below.
Tag To Test Input Only visible if 'Use Test Tag' is enabled. The tag to be tested to initiate downtime. An example would be the mass flow to a unit or area.
On_Threshold Input Only visible if 'Use Test Tag' is enabled. The value to which the Tag To Test is compared. If the value of Tag To Test is LESS THAN this threshold, then the Downtime controller will pause the Minor Maintenance and Major and Minor Failure timers. The Major Maintenance timer will continue to increment. This is independent of any downtime due to maintenance or failure.

#### Results

Tag To Test Value Display Only visible if 'Use Test Tag' is enabled. The current value of the Tag To Test.
State Value Display The current state of the equipment, expressed as a numerical value. This value could be referenced in controllers for example to perform a series of tasks depending on the state of the equipment. The States are:
• 0 = Idle;
• 1 = Running;
• 2 = Major Maintenance;
• 3 = Minor Maintenance;
• 4 = Major Failure; and
• 5 = Minor Failure.
State Display The current state of the equipment. Possible states are: Idle, Running, Major Maintenance, Minor Maintenance, Major Failure and Minor Failure.
OutputValue / Output Display The value of Tag To Set (if specified).

Total Inactive Time Calc The total amount of inactive time due to major or minor maintenance since the model was last reset.
Total DownTime Calc The total amount of down time due to major or minor failure since the model was last reset.
Total Running Time Calc The total amount of running time since the model was last reset.
Total Idle Time Calc The total amount of off time due to Tag to Test threshold being exceeded since the model was last reset.
Total Utilisation Calc The fraction of the total amount of time that the model has been Running. This includes the Idle time.
Active Utilisation Calc The fraction of the available time that the model has been Running. This excludes the Idle time.

Running Time Calc The amount of running time since the last inactive, down or off time.

## Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 DLL: ControlDyn.dll → Units/Links → Control 2: Downtime or Group: General → Units/Links → Control 2: Downtime