Tag Archives: PLC

Control Panel Layout: Top Tips with some Photos

Control panel, Systems, , ,

Amongst the control panel layout tips out there, some are practical, many are good and some are downright weird. There are is a wealth of it in the /PLC sub-reddit. Some of it is amusingly opiniated:

 

The following is my collection of top tips on control panel layouts. A few of the panel posts from Reddit are embedded below. Will add more pointers as I come across them.

 

Busbar candy
byu/Otherwise_Feed_3320 inPLC

1. Heat rises

Do the heat calculations. Enclosure vendors usually have free tools for this like this .

    • If ventilation is needed, fan at the bottom, exhaust at the top, not the other way around. Hot air rises and leaves the panel, cool air comes in the bottom.

2. Power protection components at the top. Circuit breakers, disconnects. The temperature rating on circuit breakers are usually higher than the average PLC, drive or anything that has electronics for that matter. Example here – 30A breaker from SE has an operational ambient of 158 degF/70 degC. Accessibility and safety is also better with power devices at the top. 

3. Incoming power. This really depends on the install site/location. If you have a choice, some would argue that’s it’s better for incoming power to come in from the bottom. With gravity, holes and inlets at the top of the panel have poor contingencies in the event of condensation or dirt coming in( or even water ingress- say NEMA 4/4X failure situations) . 

4. Wire labels, terminals, and wire markers

    • Avoid putting the label on the device. If the device gets replaced, the label goes with it.
    • Sometimes end users may require label on device also. Check before it gets to the FAT
    • Harmonize labelling such that it can be traced back to schematics. This will help with maintenance folks and any troubleshooting efforts.

5. Wireway

    • Vertical runs should intersect with a horizontal run such that the horizontal run stops the vertical cover from sliding down
    • Plan it out such that control wiring is separated from power wiring. If they intersect, make it perpendicular.
    • Read on to number 6.

6. Electromagnetic interference

      • Separate 480Vac and  24Vdc ( control and communications) wires. 
      • If they have to cross, it’s best done perpendicularly- ie. they cross at a 90 deg angle. Still avoid having them in proximity. Good explanation of this here
      • Additional sleeving or barriers for EMI mitigation if needed.

 

7. Spacing If the project allows for it, allow for some room between devices, PLC’s, drives, power supplies. This helps with maintenance accessibility. Also, it makes way for future expansions. More I/O if the PLC needs it, another drive …etc..

My new office 😉
byu/adi_dev inPLC

8. Ground connections

    • Spec grounding washers installed and properly torqued to bite through the paint

9. Network cabling

  • Use pre-terminated cables where possible. From a good vendor, reliability is better. 
  • From item 6 above, separate controls communications cables from the power wiring.

10. Maintenance and usability

  • Add a rack on door for reference material

 

“I´m tired boss…”
byu/andisosh inPLC

Will come back and add more as I find it…

 

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Remote PLC Connection: Connecting to a SoMachine M241 PLC using InHand Networks IG601 Cellular Gateway and Device Touch

CODESYS, PLC, Remote Access, Systems,

 

The ability to connect to a PLC remotely (or HMI) and to pull data, access webservers and download programs is increasingly a requirement on industrial automation projects. Remote data access and program maintenance saves travel time to sites and simplifies daily operations. Some of the PLC features that enable this are:

  • Webserver on PLC and HMI: Allows data monitoring and some updates to PLC configurations

 

  • WebVisualization: These are customizable user interface pages that are embedded in the PLC. WebVisu is the CODESYS term for these HTML5 pages. Some examples of their usage from YouTube are noted here.

 

  • PLC Programming software remote gateway support: This is the ability for a PLC programming software to connect to remote Ethernet based devices. This could be for program downloads or regular program viewing.

This article will cover the steps for remotely connecting from the SoMachine PLC programming software to a remote M241 PLC. The InHand Networks IG601 cellular gateway device is used as the intermediary. Other examples of intermediary gateway devices may include Netbiter by HMS and eWon ( also by HMS now I believe).

Over the last few years, the criteria I have laid out for these devices have included the means to use them without the manufacturer’s cloud- based connection service. Simultaneously, keeping the option to route more secure connections through the cloud service, only when required, is a plus.

 

The criteria for the gateway device:

 

  • Ability to setup port forwarding at the gateway device
  • Ability to use a VPN connection for secure PLC program downloads
  • Ability to support a static IP at the gateway device and allow for the above mentioned VPN connection at the same time.

The InHand Networks IG601 meets these criteria. Getting this set up can be accomplished with two sets of steps. The InHand steps and the SoMachine steps.

InHand Networks Steps:

 

  1. Connect to the InHand Device Cloud at http://g.inhandnetworks.com/. For initial setup, follow instructions per the Device Manager configuration video.

 

  1. Install Device Touch on the connecting PC. The installer is available in the Device Cloud portal. The next steps will assume proper setup of the Device Cloud and connection using Device Touch on the local PC. Instructions on Device Touch are available at the following link.

 

NOTE: While in the Device Cloud, be sure to set up a site, a device and the PLC. I forgot to add the ‘Controller’ once. It took some time and a call to InHand’s support team to figure it out.

InHandsite_Gateway_PLC
InHand Device Cloud

 

  1. Open Device Touch on your computer and connect with your Device Cloud account. Once connected to the cloud. Connect to the specific site/gateway but selecting it and clicking on the ON/OFF slider bar.

InHandDeviceTouch
Device Touch connection

SoMachine Steps

  1. In SoMachine, configure connectivity in the SoMachine gateway. The gateway is accessible by double clicking on the root of the controller directory in the device tree.

SoMachine Gateway setup for Remote PLC Connection
SoMachine Gateway

5. The connection method is set to IP address. In the example, the remote controller IP address was set to 10.0.0.100 with a subnet mask of 255.255.255.0

ConnectionMode
IP Address connection mode

    6.  Per step 3 above, if Device Touch is active and the Maintenance Channel is on/ready (screen cap below), go to the Online menu and select Login.

 

IP Address Remote PLC
IP Address Connection Mode

NOTE: The update key on the gateway will not result in the detection of the controller in the Gateway list. Entering the IP address and selecting ‘Login’ actually triggers the process if searching for the device and placing it in the available controllers list in the Gateway. The Update button in the Gateway may not find remote devices. As such, the remote PLC may not show up even if by clicking on the Update button.

 

 

  1. The gateway will scan the remote network via the Device Touch adapter. Once the controller has been found, it will show up on the controller list in the gateway with a REM icon next to it.

RemotePLCDetected
Remote PLC detected

Note: The standard warning message indicating the pending connection to a controller will pop up prior to an actual login. Entering Alt-F will proceed with the connection and potential remote download of a program. Clicking the Cancel button will abort the connection.

 

Troubleshooting tip:

Should the remote controller not be detected using the IP address connection method above, restart the SoMachine gateway as shown in the screen cap below. Subsequently repeat step 4 above.

RestartPLCGateway
Restart SoMachine Gateway

Should questions or comments arise, put it in the comments section below.

 

 

 

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PLC Programming Patterns- The Debounced Threshold/Limit

CODESYS, PAC, PLC, Programming, ,

Patterns in PLC Programming: The threshold + timer function – Debounced Threshold

PLC programs are frequently made up of the same sets of functions or patterns of logic. These patterns perform commonly required control routines. Examples include threshold detection for alarm purposes, input/output mapping and scaling functions, to name a few. These combination of functions make up re-usable patterns or function sets that form the building blocks of a PLC program.

Repeated usage of some functions in a PLC programming environment holds true to the universal 80/20 rule ;20% of the functions available in a programming environment( such as timers and logic functions) would probably be used to build 80% of PLC programs.

The debounced alarm/threshold pattern is one of these commonly required PLC programming patterns. This pattern is probably better written in ladder diagram   (instead of any of the other 61131-3 languages), for two reasons:

  • Maintenance personnel will be able to view the status of the process/monitored variable, associated timer and output all in the same place
  • It can be programmed in 2 rungs of ladder compared to more than 10 lines of code.

The ladder diagram version could look something like this:

Alarm ACTIVE
DebouncedThreshold_LD_ALARMAutoManualReset

Note: An Auto/Manual Reset Provision is built into the Alarm Reset Timer rung.

Alarm NOT ACTIVE

DebouncedThreshold_LD

The following pattern is the debounce pattern for detecting limit breaches along with a timer, written in Structured Text for the CODESYS environment. As described above, the structured text version takes more space and possibly looks more intimidating specifically to someone who is used to the ladder environment.

CODESYS-LimitThresholdScreenCap

The plain text version of the structured text version is attached below:

PROGRAM DeBounced_Limit

VAR

irProcessValue : REAL; (*Process value scaled from analog input signal*)

rProcessLowLimit : REAL; (*User defined process value low limit alarm threshold*)

qxLowLimitAlarm : BOOL;(*Low limit alarm bit*)

LowLimitAlarmTimer : TON; (*Process value low limit alarm trigger debounce timer*)

LowLimitAlarmResetTimer : TON; (*Process value low limit alarm reset debounce timer*)

LowLimitDebounceT : TIME; (*Process value low limit alarm trigger debounce time*)

LowLimitResetDebounceT : TIME; (*Process value low limit alarm reset debounce time*)

xAutoReset : BOOL;(*User enabled alarm auto reset function*)

ixUserReset : BOOL;(*User triggered alarm reset function for manual reset*)

END_VAR

(*If value is lower than low limit, start timer, else reset timer*)

IF irProcessValue < rProcessLowLimit THEN

LowLimitAlarmTimer(in:=TRUE, PT:=LowLimitDebounceT);

ELSE

LowLimitAlarmTimer(in:=FALSE);

END_IF

(*If timer lapses, trigger alarm bit*)

IF LowLimitAlarmTimer.Q THEN

qxLowLimitAlarm:=TRUE;

END_IF

(*If value is higher than low limit, start alarm reset timer, else reset debounce timer*)

IF irProcessValue > rProcessLowLimit THEN

LowLimitAlarmResetTimer(in:=TRUE, PT:=LowLimitResetDebounceT);

ELSE

LowLimitAlarmResetTimer(in:=FALSE);

END_IF

(*If timer lapses, and system permits auto-reset, reset alarm bit*)

(*If the system does not permit auto-reset, add user invoked reset bit here*)

IF LowLimitAlarmResetTimer.Q AND (xAutoReset OR ixUserReset) THEN

qxLowLimitAlarm:=FALSE;

END_IF

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CODESYS Pointers and Dereferencing

CODESYS, PAC, PLC, Programming, ,

Pointers and Arrays in CODESYS

The CODESYS language supports the usage of pointers which is essentially a variable that stores the location of another variable or data point instead of its value. The actual value of a variable that a pointer points to can be retrieved by dereferencing the pointer.

 

What could it be used for?

       1.Storing the location of the variable saves space specifically when pointing to large                 data points or structures.

  1. Pointers allow for sorting and re-arrangement of data sequences without actually changing the location of the original data points. To characterize in a diagram:

Pointers and Arrays Diagram

  1. Going down the path of object oriented programming in PLC’s/PAC’s, this supports abstraction by separating the usage, manipulation and parts of an object from the original object itself. This helps reduce the PLC code required to handle every scenario and also helps in situation where the original object can not be manipulated because its hardcoded to an input ( for example).

 

Example:

 

Let’s say the array of data on the left side of the diagram above is read (as inputs) from a set of 4 drives controlling 4 pumps. From top of the array to the bottom Array location 0 would be for Pump 1 , location 1 for Pump 2 …..location 4 for Pump 4.

 

If the data is each of the pumps runtime, the pointers to the runtime allow for it to be sorted and stored in the pointer of arrays without changing the order of the original array which is important, as the original array of runtime data may be hardcoded to the actual input or read values from the drives.

 

Secondly, when the decision is made to call a pump to run, the same mechanism of pointers and arrays and de-referencing can be used to point to the command word of each of the pumps on a communication bus.

The end result is the amount of code required in determining which of the pumps to run is reduced.

Pump Example Pointers and Arrays

What does the syntax look like in CODESYS?

To create a pointer:

The address operator or ADR is used.

Let’s say the variables are:

 

PROGRAM PLC_PRG

VAR

j: INT;

k:INT;

pointToJ: POINTER TO INT;

END_VAR

The pointer assignment would be:

 Pointer

in plain text:

pointToJ:=ADR( j);

Note: ADR is a CODESYS operator and not an operator prescribed in IEC61131-3.

 

To de-reference a pointer:

The ^ operator is used to de-reference pointers.

Example:

in plain text:

k:=pointToJ^;

This would yield the value of integer j.

SimulatedPointerDeReferencing

 

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