Start choosing a PLC by counting the input and output devices to connect: how many switch-type points and analog points, and what load each output has to drive, with some spare points on top. Then check whether program memory and scan speed are enough, then the communication ports, expansion method and form factor, and finally the programming language, the editing software and the site environment. This article is about choosing programmable logic controllers (PLCs) for machine and line control; temperature controllers, HMIs and drives have their own articles and are outside its scope.
Stage ① | Inputs and outputs: points of switch-type and analog-type, output type, spare capacity.
Stage ② | Memory and scan time: program memory, data memory, how long one scan takes.
Stage ③ | Communication and expansion: ports and protocols, local and remote I/O, brick or rack type, power supply.
Stage ④ | Programming language and environment: language, editing software, temperature and dust.
This article starts from “you have already decided to control this machine with a PLC”. Each stage below says how to do it, what public sources say and what Jiahon can help with; sources, exceptions and arrangement are in the notes at the end. This is the general case and still depends on the individual case.
Figure 1. The four stages of PLC selection (schematic, not to scale)
① Inputs and outputs. Switch-type and analog-type: count separately, then split AC and DC. Output type: relay or transistor. Spare points: leave margin, round up to module sizes. Done when: the points and output type are settled.
② Memory and scan. Program memory: estimate words, then add spare. Data memory: setpoints, present values, flags. Scan time: processor and instruction speed. Done when: it fits and runs fast enough.
③ Communication and expansion. Ports and protocols: the equipment you connect to speaks the same one. Local or remote: long distances need remote I/O support. Form and power: brick or rack. Done when: it connects and can be expanded.
④ Language and environment. Programming language: ladder, structured text, etc. Editing software: enough instructions, one you know. Site environment: temperature, dust, vibration. Done when: it can be written and it can survive on site.
Stage ①: inputs and outputs, count the devices first, then see what the outputs can drive
How to do it:
Count the devices to connect in two classes: switch-type (just two values, on or off) and analog-type (any value in a range, such as pressure, temperature, flow and weight). Then split by AC or DC.
For analog signals, confirm the module supports your signal type: the common ones are 0 to 10 V voltage or 4 to 20 mA current.
Leave margin in the point count, and round up to the module’s point size.
Look at the output type: relay outputs can switch AC or DC, resistive or inductive loads; transistor outputs can switch DC just, and switch fast. The rating of each output must be greater than the load’s rated current.
A transistor output leaks a little when off, which may keep an inductive load or an indicator lamp from turning off completely.
What public sources say:
A selection guide from an automation components maker (the maker’s material, no date shown) says: first count how many switch-type devices the system has and of what kind (AC, DC and so on), and count the analog-type in the same way; the controller you choose must support your number of inputs and outputs.
An online encyclopedia entry says: switch-type has just two values, on or off; analog-type can be any value in a range, and pressure, temperature, flow and weight are often analog; a 0 to 10 V voltage input or 4 to 20 mA current input is converted into an integer from 0 to 32,767.
A knowledge-base article from an online industrial equipment seller (page shows published 5 September 2026, modified 23 September; the page says it is general information and not engineering advice, and carries product promotion) says: add 10% to 15% spare points, then round up to the module’s point size; the rating of each output must be greater than the load’s rated current (note table 1).
Another knowledge-base article from the same seller (31 July 2026) lists: relay output, about 2 to 5 A (240 V AC or 24 V DC), acting in about 10 to 20 ms, can switch AC and DC and resistive and inductive loads; transistor output, about 0.5 to 2 A (24 V DC), acting in about 0.1 to 1 ms, DC loads just; AC loads, high inrush current and the need for full isolation are listed as uses for relay outputs; switching faster than 10 to 20 times per second, pulse-width modulation and pulse outputs need transistor outputs; the leakage of a transistor output when off is about 0.1 to 1 mA and may keep an inductive load or an LED indicator from turning off completely, and the article suggests a bleeder resistor of 10 kΩ to 47 kΩ across the load (note table 2).
What Jiahon can help with:
PLC modules: the product page lists 6 models, including two 8-point analog input modules (the page says they support 4 to 20 mA current and 0 to 10 V or ±10 V voltage, and can also connect RTDs or thermocouples), one analog input module for RTDs, one 16-point relay-contact output expansion module (the page says it can switch AC solenoid valves and contactors), and one CPU unit, which the page says has 14 built-in inputs, 10 outputs and 2 analog inputs. Whether this CPU’s outputs are relay or transistor, and the rated current per relay output point, are not on the product page; please inquire.
PLC input/output modules: the product page lists a 16-point relay output module (24 V DC / 240 V AC, 2 A per point; the page says it can drive solenoid valves, indicator lamps or small motor contactors directly) and an 8-point 24 V DC input module; there are also two CPUs, one with 14 inputs, 10 outputs and 2 analog inputs, one with 20 inputs and 16 outputs. The output type of the two CPUs is not on the product page; please inquire.
PLC expansion modules: the product page lists a module with 4 analog inputs and 2 analog outputs (14-bit; the page says −10 to 10 V / 20 mA, accuracy ±1%) and a 6-channel RTD temperature module (the page says it supports Pt100 and Pt1000, 3-wire, resolution 0.1 or 1 °C, scan 1 to 2 seconds).
Stage ②: memory and scan time, the program fits and runs fast enough
How to do it:
First understand how a PLC works: it repeats three things round after round, read inputs, execute the program, write outputs. The time one round takes is the scan time.
Look at scan speed: look at the processor’s speed and also at how fast each kind of instruction executes; some CPUs are fast at logic and slow at data-handling instructions.
Estimate program memory: first estimate the real number of words needed, then add spare; how many words each instruction takes follows the product manual.
Look at data memory: timer and counter setpoints and flags all have to be stored; if you need to keep history, the size of the data table may decide the CPU model.
If the scan is too slow, or you have to count very fast pulses, use a separate counting module, whose counting does not depend on how fast the program executes; remote I/O makes response time less certain.
Figure 2. One PLC scan (schematic, not to scale): Read inputs (read the field inputs in) → Execute program (calculate once through the program) → Write outputs (send the result to the outputs) → one round done, start the next round at once. The time one round takes is the scan time. Remote I/O makes response time less certain; where the scan is too slow, a separate counting module can be used.
What public sources say: The online encyclopedia entry says: a PLC repeats the three steps of reading inputs, executing the program and writing outputs; evaluating all instructions and updating outputs usually takes tens of milliseconds; remote I/O adds uncertainty to response time; where the scan time is too long (for example pulses from a shaft encoder), a separate counting module is used, and counting pulses does not depend on how fast the program executes; the program is usually kept in battery-backed or non-volatile memory. The selection guide from the automation components maker above says: look at both processor speed and instruction execution speed, as some CPUs are faster at Boolean logic and slower at data-handling instructions; the rule of thumb for program memory is about 5 words per switch-type device and about 25 words per analog-type device, for applications that are basically sequential, and complex applications are harder to estimate; timer and counter instructions use data memory to store the setpoint, present value and other internal flags, and when history must be kept, the size of the data table may decide which CPU you choose. The knowledge-base article from the online seller above says: first estimate the real number of program words and then add 25% spare; logic instructions often take 1 word, and timing, counting, shift, math and data-move instructions often take 2 words, and how many words each instruction takes follows the product manual (note tables 1 and 3).
What Jiahon can help with:
PLC series page: just one CPU on the page states program capacity: 64K steps, 48 I/O points (the page also says built-in 3-axis positioning, 100 kHz); the other CPU modules on the page are listed by name just and the memory is not on the product page; please inquire.
PLC modules: the page says one CPU has 12 KB of work memory (the page notes this is the general case) and another 100 KB; the page’s series comparison table gives the work memory range of three series as 12 to 512 KB, 100 to 150 KB, and 500 KB to 60 MB and above.
PLC CPU and power supply modules: the page says this CPU has 2 MB of memory.
PLC expansion modules: the page lists a program memory cassette: program 20K words, data 20K words, 1M-bit flash memory, with a write-protect switch; the page says it is used to back up and restore programs quickly.
PLC technology module series: the page lists a high-speed counting technology module: 32-bit counting, for incremental encoders (A, B, N phases), 3 inputs and 2 outputs, for high-speed counting, speed measurement and position control.
The pages use different memory units (steps, words, KB, MB) and cannot be compared directly; CPU scan time and instruction execution speed are not on any page, so please inquire.
Stage ③: communication and expansion, it connects to other equipment and can be expanded
How to do it:
Communication ports: list first the networks, drives and HMIs you need to connect. Ports other than the programming port are not necessarily on every unit; confirm the CPU has the ports you need, and if not, add a communication module.
Protocols: built-in ports are commonly USB, Ethernet and several serial ports; industrial protocols are many and many are brand-specific, so confirm the equipment you connect speaks the same one.
Local or remote: is all the I/O inside the control cabinet, or is some spread around the machine, far from the CPU? For long distances choose a controller that supports remote I/O, and confirm the distance and speed are sufficient. Ethernet I/O may need a specific protocol.
Form: a brick type (processor and I/O in one housing, often with expansion modules) saves panel space; a rack type (a rack holds the power supply, processor, I/O and communication modules) lets one processor manage several racks and thousands of points.
Power: add up the consumption of the CPU, every I/O module and special module, then choose a rating about 30% higher; when the main unit and expansion units share a power supply, the line voltage drop must be below 0.25 V.
Figure 3. Brick type and rack type. Brick type: the processor and I/O are in one housing (power supply, processor, I/O, with expansion modules), a smaller form that saves panel space. Rack type: a rack holds the power supply, processor and various modules (power supply, processor, input, output, communication), and one processor can manage several racks.
What public sources say: The selection guide from the automation components maker above says: ports other than the programming port are not necessarily on every controller, so choose a CPU that supports your communication needs and add a communication module if necessary; decide first whether to use local I/O just or also remote I/O, and for long distances choose a controller that supports remote I/O and check that distance and speed are sufficient; Ethernet I/O may need a specific protocol, such as Modbus; a smaller form saves a lot of panel space. The online encyclopedia entry says: the brick type (the article calls it a brick) puts all units in one housing, and expansion I/O modules are usually available; the rack type has a rack, which holds the power supply, processor, I/O modules and communication interfaces, one processor can manage several racks, and there can be thousands of inputs and outputs; built-in ports are commonly USB, Ethernet, RS-232, RS-485 and RS-422, and protocols include Modbus and EtherNet/IP, many of them brand-specific. The knowledge-base article from the online seller above says: add up the consumption of the CPU, every I/O module and special module, and choose a rating about 30% higher; when one power supply feeds the main unit and expansion units, the line voltage drop from the main unit to the last expansion unit must be below 0.25 V, and the limits of each module must be confirmed in the product manual (note table 3).
What Jiahon can help with:
PLC series page: the page lists both brick-type CPUs (the page says 48-point and 40-point I/O) and, for rack use, a main base, extension bases, power supply modules, CPU modules and I/O modules; for communication it lists an Ethernet module, network communication modules, and remote input, output and analog modules on an industrial network (the page says this network supports expansion of distributed I/O).
PLC expansion modules: the page lists three communication expansion boards: a two-port RS-485 (baud rate 4,800 to 921,600 bps, supporting that series’ own protocol and Modbus RTU/ASCII), a single-port RS-485, and an Ethernet expansion board (10BaseT, TCP/IP, Modbus-TCP, with an additional RS-485 interface).
PLC component series: the page lists two CPUs (the page says 14 inputs / 10 outputs, or 30 inputs / 20 outputs, with interfaces for industrial Ethernet and a fieldbus), bases and modules for distributed I/O, 24 V DC power modules of 2 A and 10 A, and 20-pin and 40-pin front connectors.
PLC CPU and power supply modules: the page says this CPU has two EtherNet/IP Ethernet ports and connects up to 16 I/O modules and 32 network nodes; a backplane power module of 4 A (5 V DC); and a DIN rail power supply, 24 V DC 2.5 A (60 W, 85 to 264 V AC input).
The power consumption of each module and the voltage-drop limit from the main unit to an expansion unit are not on the product pages; please inquire.
Stage ④: programming language and environment, it can be written, changed and survive on site
How to do it:
Programming language: the languages of the international standard IEC 61131-3 are ladder diagram and function block diagram (graphical), structured text and instruction list (textual), plus sequential function chart, which is used to organize the program.
Choose the language by the job: basic switch-type logic in ladder diagram, which people with an electrical background can also read; complex math, process control and data analysis in structured text; repeatable multi-step actions in sequential function chart.
Editing software: see whether you want standard instructions or need special instructions (for example a built-in PID); whether addresses are fixed or named; choose a language and software you know, and development, debugging and maintenance will go more smoothly.
Site environment: temperature, dust, vibration and any regulations specific to the plant must match the model’s specifications.
With existing equipment: confirm that a new controller can work with the products already in the plant, as some controller products cannot interoperate.
What public sources say:
The IEC 61131-3 page of PLCopen, the international PLC standards organization, says: edition 3.0 of the standard (2013) has two textual languages (instruction list, structured text) and two graphical languages (ladder diagram, function block diagram), and has sequential function chart elements to organize programs and function blocks; the page does not say instruction list is deprecated and does not include the full standard text.
A 2010 trade media article (the page is credited to the Australian arm of an automation vendor) says: ladder diagram is used in “probably” 95% of applications (the article’s own estimate, with no source), non-programmers with an electrical background can read the program, but PID, trigonometry and data analysis are hard to implement, and a large program needs good documentation to be readable; structured text makes trigonometry, calculus and data analysis much easier than ladder and instruction list, the program is more compact than ladder and runs faster, but many experienced programmers and maintenance people are not familiar with it and debugging is inconvenient, and it is often used in the background; sequential function chart is for repeatable multi-step processes and maintenance people find it easy to understand, but it executes more slowly than the other languages; functions written in different languages can call each other, for example wrapping a structured text program as one instruction and calling it in ladder.
The online encyclopedia entry says the standard has two textual languages and three graphical languages (including sequential function chart), and that instruction list was classed as deprecated in the third edition.
The selection guide from the automation components maker above says: decide whether to use traditional standard instructions or special ones, with a built-in PID easier to use than writing your own; choose fixed or named addresses; choose programming software you are familiar with; for the environment look at temperature, dust, vibration and regulations specific to the plant, and the usual operating temperature of common controllers is about 0 to 55 °C (32 to 130 °F); some controller products cannot interoperate, so confirm they work with existing products (note table 4).
What Jiahon can help with:
PLC modules: the page says that when moving from an old series to a new series, use the migration tool of the new edition of the editing software, test-migrate one non-critical line first, and keep the old software environment until the whole plant has migrated; it also says that the revision number at the end of the model number sometimes means firmware changes in a new revision, so for critical spares buy the same revision, and run a full functional test after replacement. The page also says 3 of the models belong to an old series already announced as discontinued, mainly for downtime spare needs, with new projects advised to prefer the new series (the page says to check the maker’s published information for the schedule of individual models).
PLC, sensor, safety and relay components: the page says communication protocols between different brands may not interoperate, and the choice of communication gateway deserves attention in integration; the page also lists several serial and network communication modules, which it says can serve as cross-brand integration interfaces.
Which programming languages are supported, the editing software and its licence, operating temperature, dust protection and vibration resistance are not on any page; please inquire.
To match a model, please prepare five items: the number of inputs and outputs (switch-type and analog-type, AC or DC), the load each output must drive, the networks and equipment to connect, the expected program size and scan requirement, and the installation environment. Please contact Jiahon.
Further reading: How a temperature controller differs from a PLC, PLC vs HMI, PLC vs relay, PLC vs VFD
On SMT / EMS lines: equipment connection, error-proofing and data collection
PLCs and peripheral connections on SMT equipment. Loaders, buffers, conveyors and washers are mostly controlled by PLCs and hand boards in and out to each other with SMEMA signals; placement machines, printers and AOI each have their own controllers and upload data through a communication interface (stage ③ of this article).
Error-proofing systems depend on equipment connection. In a PFMEA of an SMT line from engineering records, “wrong reel / feeder loaded” relied on double checking with a detection score of 5, which fell to 2 after an IT error-proofing system was added; a placement output improvement plan had the first placement machine scan bad-board marks and pass the information over the intranet to the two machines after it, saving about 6 seconds of repeated checking per board. Improvements like these require the equipment to be able to communicate outward.
Industry communication standards. Semiconductor equipment commonly uses SEMI SECS/GEM (SEMI E30 GEM); the electronics assembly industry has in recent years promoted IPC-CFX so that equipment of different brands exchange data in one message format. When choosing a PLC, first ask which one the MES or data platform you will connect supports.
Notes: sources and exceptions
This part is for readers who need to check; the practices above stand without it. When your machine specification, the PLC’s written specifications or safety standards differ from this article, follow them.
Sources for each stage
| Source | Stages and content used | Where it comes from |
|---|---|---|
| Source 1 | Stages ① to ④: I/O, program and data memory, scan speed, ports, remote I/O, form, software, environment, existing products | A selection guide from an automation components maker (the maker’s material, no date shown) |
| Source 2 | Stage ④: IEC 61131-3 languages and edition | The IEC 61131-3 page of PLCopen, the international PLC standards organization (edition 3.0, 2013; just the introduction page was read, not the full standard) |
| Source 3 | Stage ④: use and limits of each language, mixing | An article from a trade media outlet (15 March 2010; the page is credited to the Australian arm of an automation vendor; fairly old) |
| Source 4 | Stages ① to ④: signals, one scan, form, ports and protocols, instruction list | The online encyclopedia’s PLC entry (edited by many people, changes over time) |
| Source 5 | Stages ① to ③: spare points, output rating, program words, power | A knowledge-base article from an online industrial equipment seller (published 5 September 2026, modified 23 September; carries product promotion) |
| Source 6 | Stage ①: relay outputs and transistor outputs | Another knowledge-base article from the same seller (31 July 2026; carries product promotion) |
| Jiahon material | “What Jiahon can help with” | Jiahon product pages |
Table 1 | I/O and memory
| Item | Content | Source |
|---|---|---|
| How to count I/O | Count switch-type and analog-type separately, split AC and DC; the controller you choose must support the number of inputs and outputs | Source 1 |
| Signals | Switch-type is just on or off; analog-type can be any value in a range (pressure, temperature, flow, weight); 0 to 10 V or 4 to 20 mA is converted into an integer from 0 to 32,767 | Source 4 |
| Spare and output rating | Add 10% to 15% to the points and round up to module point sizes; each output rating greater than the load’s rated current | Source 5 |
| Program memory | About 5 words per switch-type device and about 25 per analog-type (basically sequential applications, complex ones are harder to estimate); the other: estimate real words and add 25% spare, logic instructions often 1 word, timing, counting, shift, math and data-move often 2, follow the product manual | Sources 1, 5 |
| Data memory | Stores setpoints, present values and flags; to keep history, data table size may decide the CPU model | Source 1 |
Table 2 | Output types (source 6, knowledge-base article of an online seller)
| Item | Relay output | Transistor output |
|---|---|---|
| Current (range the article lists) | About 2 to 5 A (240 V AC or 24 V DC) | About 0.5 to 2 A (24 V DC) |
| Action time | About 10 to 20 ms | About 0.1 to 1 ms |
| Load | AC and DC, resistive and inductive | DC just |
| Uses the article lists | AC loads, high inrush current, full isolation needed | Switching faster than 10 to 20 times per second, pulse-width modulation, pulse output, high-frequency operation |
| When off | — | Leakage about 0.1 to 1 mA, may keep an inductive load or indicator from turning off completely; the article suggests a bleeder resistor of 10 kΩ to 47 kΩ |
| Reminder | The article ends by stating it is general information and not engineering advice; it carries product promotion |
Table 3 | Scan, communication and expansion
| Item | Content | Source |
|---|---|---|
| One scan | Read inputs, execute program, write outputs; evaluating instructions and updating outputs usually takes tens of milliseconds; remote I/O adds uncertainty to response; where the scan is too long use a separate counting module; the program is kept in battery-backed or non-volatile memory | Source 4 |
| Scan speed | Look at processor speed and instruction execution speed; some CPUs are faster at Boolean logic and slower at data-handling instructions | Source 1 |
| Communication ports | Ports other than the programming port are not always included; choose a CPU that supports the need, or add a communication module | Source 1 |
| Built-in ports and protocols | USB, Ethernet, RS-232, RS-485, RS-422; protocols include Modbus, EtherNet/IP, many brand-specific | Source 4 |
| Remote I/O | For long distances choose a controller that supports remote I/O; check distance and speed; Ethernet I/O may need a specific protocol, such as Modbus | Source 1 |
| Form | Brick: units in one housing, often with expansion modules, saves panel space. Rack: power supply, processor, I/O and communication modules on a rack, several racks and thousands of points possible | Sources 1, 4 |
| Power | Add up module consumption and choose a rating about 30% higher; voltage drop from the main unit to the last expansion unit below 0.25 V; confirm module limits in the product manual | Source 5 |
Table 4 | Programming language and environment
| Item | Content | Source |
|---|---|---|
| IEC 61131-3 | Edition 3.0 (2013): textual languages (instruction list, structured text), graphical languages (ladder diagram, function block diagram), sequential function chart elements; the page does not say instruction list is deprecated | Source 2 |
| Ladder diagram | Used in “probably” 95% of applications (the article’s own estimate); readable by people with an electrical background; PID, trigonometry and data analysis are hard to implement; large programs need good documentation | Source 3 |
| Structured text | Easier for trigonometry, calculus and data analysis; more compact and faster than ladder; many experienced people and maintenance staff are not familiar with it; debugging is inconvenient | Source 3 |
| Sequential function chart | Repeatable multi-step processes; maintenance people find it easy to understand; executes more slowly | Source 3 |
| Mixing | Functions written in different languages can call each other, for example calling structured text wrapped as an instruction in ladder | Source 3 |
| Instruction list | Classed as deprecated in the third edition | Source 4 |
| Software | Traditional standard instructions or special instructions (a built-in PID is easier than writing your own); fixed or named addresses; choose familiar software | Source 1 |
| Environment | Temperature, dust, vibration, plant-specific regulations; common operating temperature about 0 to 55 °C (32 to 130 °F) | Source 1 |
| Existing products | Some controller products cannot interoperate; confirm they work with existing products | Source 1 |
Standards
The standards cited here should be checked against the current edition from the issuing body.
- IEC 61131-3, programming languages for programmable controllers (source 2 is PLCopen’s introduction page; this article did not read the full standard). Issuer: IEC (International Electrotechnical Commission).
This is the general case and still depends on the individual situation.
Exceptions and limits
What was and was not seen: The sources are 1 selection guide from an automation components maker (the maker’s material, no date shown), 1 PLCopen standard introduction page, 1 trade media article from 2010, 1 online encyclopedia entry, and 2 knowledge-base articles from the same online industrial equipment seller (2026). The full text of the IEC 61131 series was not read, and no datasheet of any Jiahon product was read.
Sources with a position: Source 1 is the maker’s material; sources 5 and 6 are published by an online seller, carry product promotion, and the pages themselves state they are general information and not engineering advice; the page of source 3 is credited to an automation vendor; source 4 is an online encyclopedia edited by many people and its content changes. This article takes just the general statements and the numbers they give themselves.
Numbers are examples: Spare ratios, memory words, current and action times, bleeder resistor, power margin, voltage drop and operating temperature are all the sources’ examples or rules of thumb, not selection thresholds; different plants and models will differ. “Ladder diagram about 95%” is source 3’s own estimate, with no source cited.
On languages: Source 2 writes sequential function chart as an element for organizing programs, while source 4 counts it as a fifth language; this article gives both.
Conversion: The Fahrenheit conversion is the one source 1 itself lists (0 to 55 °C is 32 to 130 °F).
This article’s arrangement: This article adds no practice beyond the sources; “the time one round takes is the scan time” is wording arranged from the sources’ description; “the pages use different memory units and cannot be compared directly” is an arrangement of how the product pages are written. The other sentences can all be matched to statements in the sources.
Standard name: IEC 61131-3 was read just through PLCopen’s introduction page; the full standard was not read.
Scope: This article covers just the general order for choosing a PLC for machine and line control; it does not compare brands and models, safety PLCs or motion control, and does not cover prices and lead times.
Equipment and products: The numbers and statements under “What Jiahon can help with” were read as text from the product pages on 13 October 2026, without looking at product images and without reading any datasheet; they were not verified by this article; specifications follow the product pages, and where a product page is silent, please inquire. Model numbers, series codes and brands on the product pages are not given here, and the link text uses function names; the “also see”, “application scenarios” and marketing text on the product pages are the pages’ own and are not cited. The PLC series page also lists HMIs on the same page; the “PLC, sensor, safety and relay components” page also lists sensors, safety components and relays on the same page, and this article uses just what it says about communication. The discontinuation and migration statements on the PLC modules page are the product page’s own and were not separately verified. Please inquire about stock.
This article is a summary of the general case. It is not a paraphrase of standard text, not an endorsement of any one vendor, equipment maker or service provider, and not an assurance for your equipment or process. Follow your machine specification, the PLC’s written specifications and safety standards, and your own verification. This is the general case and still depends on the individual situation.