The Downtime unit operation can be used to simulate downtime of a piece of equipment due to maintenance and/or failure or other causes. The model allows one tag to be set to different values depending on whether the unit is active or inactive due to maintenance or failure. One tag can also be tested and if above a defined threshold, the unit can be deactivated.
The Probability Density functions used for the times between major and minor failures and the times to complete the repairs are as follows:
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.
|
Tag / Symbol
|
Input / Calc
|
Description/Calculated Variables / Options
|
|
Common First Data Section
|
General Unit Requirements
|
| On | Tick box | Switch the unit on (ticked) or off (cleared).
|
| SetTagAlways | 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.
|
| IntegralPeriod | 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 stepsize of the project. For example, if the step size is 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.
|
| IntegralInactivePeriod | 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 stepsize 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.
|
| Count | Input | The number of independent downtime blocks required. This may be any number from 0 up to 20. The user may also change this number at any time except when the model is running. 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.
|
|
|
| TotalTime | Output |
|
| Reset_All | Button | This will reset the results values and restart any offsets.
|
| Auto_Reset | Tick box | If ticked, the results and offsets will be reset at the beginning of every time the model is rerun.
|
Individual Downtime Blocks (T0, T1, etc)
Each independent downtime block has the following layout. Each block will be on a separate tab page.
|
| Requirements...
|
| Desc | Input | Optional downtime block description.
|
| Failure Options | None | Do not include any failure settings.
|
| Major | Include Major failure settings only.
|
| Minor | Include Minor failure settings only.
|
| Major & Minor | Include Major and Minor failure settings.
|
| T.[Downtime Block number].MajorMaint...
|
| 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.
|
| RqdInactivePeriod | Input | The time period of the downtime for major maintenance, i.e. the period during which the equipment is inactive.
|
| Period | Output | 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 IntegralPeriod option has been selected.
|
| InactivePeriod | Output | 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 IntegralInactivePeriod option has been selected.
|
| T.[Downtime Block number].MinorMaint...
|
| 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.
|
| RqdInactivePeriod | Input | Minor Maintenance Required Inactive Period - The time period of the downtime for minor maintenance, ie. how long the equipment is inactive.
|
| Period | Output | 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.
|
| InactivePeriod | Output | Minor Maintenance - The time period of the downtime for minor maintenance, i.e. how long the equipment is inactive.
|
| T.[Downtime Block number].MajorFailure...
|
| UptimePDF | 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.
|
| UptimeAverage | Input | The average time (Tavg) that the equipment runs without a major failure.
|
| UptimeDeviation | Input | The deviation (dev) 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.
|
| DowntimePDF | 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
|
| DowntimeAverage | Input | The average time (Tavg) that the equipment is inactive due to a major failure.
|
| DowntimeDeviation | Input | The deviation (dev) 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.
|
| T.[Downtime Block number].MinorFailure...
|
| UptimePDF | 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
|
| UptimeAverage | Input | The average time that the equipment runs without a minor failure.
|
| UptimeDeviation | Input | The deviation from the average time that the equipment runs without a minor failure. This is only used if a constant or normal Probability Density Function (PDF) is chosen.
|
| DowntimePDF | 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
|
| DowntimeAverage | Input | The average time that the equipment is inactive due to a minor failure.
|
| DowntimeDeviation | Input | The deviation from the average time that the equipment is inactive due to a minor failure. This is only used if a constant or normal Probability Density Function (PDF) is chosen.
|
| T.[Downtime Block number]...
|
|
|
| Requirements...
|
| 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.
|
| InactiveVal | Input | The value to set tag to (see below) when equipment is inactive due to maintenance or failure. This input is optional.
|
| TagToSet | 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.
|
| TagToTest | Input | The tag to be tested to initiate downtime. This input is optional. An example would be the number of hours a unit has been running.
|
| On_Threshold | Input | The value for TagToTest to be compared to. This input is optional. If the value of TagToTest exceeds this threshold, then the unit will become inactive. This is independent of any downtime due to maintenance or failure.
|
|
|
| Results...
|
| If a TagToTest has been specified
|
| TagToTestValue | Output | The current value of the TagToTest (if one has been specified).
|
| StateValue | Output | The current state of the equipment (as defined above), expressed as a numerical value. This value could be referenced in PGMs for example to perform a series of tasks depending on the state of the equipment. The meaning of the numbers is 0=Minor Maintenance, 1=Major Maintenance, 2=Minor Failure, 3=Major Failure, 4=Running, 5=Off
|
| State | Output | The current state of the equipment. Possible states are: Minor Maintenance, Major Maintenance, Minor Failure, Major Failure, Running or Off.
|
| Output | Output | The value that TagToSet is set to (if specified).
|
|
|
| TotalInactiveTime | Output | The total amount of inactive time due to major or minor maintenance since the model was last reset.
|
| TotalDownTime | Output | The total amount of down time due to major or minor failure since the model was last reset.
|
| TotalRunningTime | Output | The total amount of running time since the model was last reset.
|
| TotalOffTime | Output | The total amount of off time due to TagtoTest threshold being exceeded since the model was last reset.
|
|
|
| RunningTime | Output | The amount of running time since the last inactive, down or off time.
|
if Tavg - dev <= t <= Tavg + dev
(note: deviation is not used in this model)
