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PLC HMI Machine Control Upgrade Guide for Coolmay Systems
An ageing machine can still cut, fill, press, clamp or convey perfectly well while its control system becomes the part everyone worries about. The mechanics are familiar, but the wiring is brittle, the drawings are out of date and the operator panel no longer explains what the machine is doing.
A combined PLC and HMI can be a practical way to renew that control system without building a large separate panel architecture. Coolmay combined HMI and PLC units bring the operator display and control hardware into one compact package, which suits many small to medium machine upgrades.
The risk is starting in the wrong place. A good upgrade does not begin by copying old screens or buying a controller that looks about right. It begins by documenting how the machine actually works.
Start with the machine sequence before choosing hardware
A successful PLC HMI machine control upgrade depends on understanding the operating sequence in plain terms. That means recording what the machine must do, when it must do it and what should stop it from doing something unsafe or damaging.
Old drawings help, but they rarely tell the full story. Machines gather changes over years. A sensor gets replaced with a different type. A timer is adjusted to work around a sticky cylinder. An operator learns to press two buttons in a certain order because the original sequence never handled a product variation well.
Before selecting a Coolmay unit, write down the machine sequence from the machine itself.
Capture at least these items:
Operating modes such as manual, automatic, jog, set-up and clean-out
Start conditions for each mode
Permissives that must be true before movement or heating can begin
Step-by-step automatic sequence
Normal stop behaviour
Emergency stop behaviour
Power failure and restart behaviour
Fault detection and reset behaviour
Product changeover settings
Operator adjustments and limits
For example, a filling machine may need an infeed sensor, container-present sensor, nozzle-down confirmation, fill valve output, flow pulse input and reject signal. The old screen may only show “Run” and “Fault”, but the real control task contains many more decisions.
Speak with operators and maintenance staff early. They often know the awkward workarounds that never made it into the electrical drawings. These details can be the difference between a smooth changeover and a machine that technically works but frustrates everyone on shift.
Build a signal schedule that reflects the real machine
Once the sequence is clear, turn it into a signal schedule. This is the bridge between process knowledge and hardware choice.
A signal schedule lists every input and output the controller must handle. It should include more than the point name. Add enough detail to select the right hardware and design the wiring properly.
A useful signal schedule includes:
Item | What to record | Why it matters |
Digital inputs | Sensor type, voltage, switching logic and location | Confirms compatibility with the PLC input circuit |
Digital outputs | Load type, current, voltage and switching frequency | Helps choose relay, transistor or interposing hardware |
Analogue inputs | Signal type, range, units and scaling | Prevents mismatched current, voltage or temperature inputs |
Analogue outputs | Signal type, load and controlled device | Confirms the controller can command the field device |
Communications | Protocol, wiring type, baud rate and device address | Avoids surprises with drives, meters and remote devices |
Spare capacity | Future sensors, outputs and analogue points | Leaves room for minor changes after commissioning |
Coolmay combined HMI and PLC ranges include different model variants with different input and output counts, analogue channel options, communications ports and output types. Select from the completed signal schedule, not from a rough memory of the machine.
Allow sensible spare capacity. A controller that uses every I/O point on day one leaves no space for a guard switch change, an added sensor or a future counting signal. Spare points also make commissioning easier when a small design change becomes the cleanest fix.
Match output types to the loads being controlled
Output selection deserves close attention. Relay and transistor outputs serve different purposes, and neither should be treated as a universal switch for every load.
Relay outputs are useful where isolated switching is needed and output speed is modest. They can suit many simple on/off loads when the electrical rating matches the device being switched. They are mechanical contacts, so they wear with use and are not ideal for high-speed pulsing.
Transistor outputs suit fast DC switching and repeated operation. They are often used for smaller DC loads, pulses and signals to other control devices. They normally do not provide the same contact isolation as a relay output, and polarity matters.
Do not assume a controller output can directly operate a motor, large solenoid, brake, heater or proportional valve. In many cases, the PLC output should command an interposing relay, contactor, solid-state relay, valve driver or drive input instead.
Protection also matters. Inductive loads such as contactor coils and solenoids can create electrical noise and voltage spikes when switched. Suitable suppression protects the controller and reduces nuisance faults. The right answer depends on the load, supply type and manufacturer requirements.
A practical output review asks four questions:
What voltage and current does the load require?
How often will the output switch?
Does the load need isolation, suppression or a driver?
What should happen if the controller loses power or faults?
The last question is easy to miss. Some outputs should drop out immediately on fault. Others may need a controlled stop through external safety-rated hardware. The PLC program is only one part of that behaviour.
Confirm input signal types and analogue scaling
Inputs can create upgrade problems when they are treated as simple on/off points. Even a basic sensor needs the right voltage, wiring method and logic.
Check whether digital sensors are PNP or NPN, normally open or normally closed, two-wire or three-wire. Confirm the supply voltage and whether the existing wiring can be reused. A sensor that worked with the old controller may not suit the new input arrangement without a wiring change or interface device.
Analogue inputs need even more care. A pressure transmitter with a 4 to 20 mA current output needs a compatible current input. A device with a 0 to 10 V signal needs a voltage input. Temperature sensors, load cells and special measurement devices may need dedicated modules or signal conditioners.
Scaling should be documented in engineering units. For example:
Signal | Electrical range | Engineering range | Display unit |
Tank pressure | 4 to 20 mA | 0 to 600 kPa | kPa |
Conveyor speed request | 0 to 10 V | 0 to 45 m/min | m/min |
Product weight | Signal conditioned | 0 to 25 kg | kg |
This makes the HMI clearer and reduces maintenance confusion. A technician should not need to guess whether a value of `3276` means low pressure, half scale or a failed transmitter.
Analogue alarms should also use real units. “Pressure low at 120 kPa” is far more helpful than “AI1 less than 6400”.
Verify serial and network communications early
Many older machines include drives, temperature controllers, weighing instruments, barcode scanners or meters connected through serial communications. These links can be harder to replace than discrete wiring because the details are often poorly documented.
Record the protocol, wiring standard and communication settings before committing to hardware. This may include RS-232, RS-485, Modbus RTU or another supported protocol. Also record baud rate, parity, stop bits, device address and register map where relevant.
Protocol support should be verified against the actual device documentation. A port that uses the same connector does not guarantee that the controller can talk to the device in the required way.
Where the existing protocol is uncertain, plan testing time. It is better to discover a communication issue on the bench than during a short shutdown window.
Design the HMI around operation, not decoration
The HMI should make the machine easier to run and maintain. That does not mean copying the old screen layout pixel for pixel.
Start with the tasks operators perform most often:
Start and stop the machine
Select manual or automatic mode
View current step or process state
Adjust approved setpoints
See active faults
Reset faults once the cause has been corrected
Run manual movements during set-up or maintenance
A good screen tells the operator what the machine is waiting for. If the start button does nothing because a guard is open, an air pressure switch is off or a reject bin is full, the HMI should say so. This reduces guesswork and avoids unnecessary calls to maintenance.
Use clear labels. Match field device names to the electrical drawings and I/O schedule. If the input is called `PE102 Container Present` in the program, avoid calling it “Sensor 4” on the HMI.
For manual screens, separate movement commands by function and include status feedback. A valve output button without cylinder position feedback gives only half the story.
Plan fault handling before commissioning
Fault handling should be part of the functional design, not a patch added after the first trial.
Document each fault with:
The condition that triggers it
The action the machine takes
The message shown to the operator
The reset condition
Whether the event should be latched
Any fault delay needed to avoid false trips
For example, “No product detected” may stop the cycle at the next safe point, while “Guard opened” may remove motion energy through the safety circuit and require a deliberate reset. Treat these as different events with different responses.
Avoid vague HMI messages such as “System fault”. A message like “No fill confirmation after valve open” gives maintenance a place to start.
Also decide how the machine should recover after power loss. Some machines can restart from a known home position. Others need an operator-guided recovery sequence to clear product, return axes or vent pressure. Document this clearly and test it.
The best upgrade is not the one with the flashiest screen. It is the one where the machine state, fault cause and next safe action are obvious.
Keep safety functions separate and checked
A PLC and HMI upgrade must not weaken machine safety. Emergency stops, guards, light curtains, safety gates and high-risk motion functions may require safety-rated relays or safety controllers. A standard PLC output is not a substitute for a required safety function.
Review the existing safety design before changing the control system. If the original machine has no current risk assessment, the upgrade is a good time to arrange one with a competent person.
In Australian workplaces, machine safety obligations sit under work health and safety duties as well as relevant standards and site requirements. The details vary by machine and application, so the control upgrade should be assessed in context.
At a practical level, confirm:
Emergency stop devices are correctly wired and tested
Guard switches behave as intended
Dangerous motion stops in the required way
Stored energy is controlled
Reset actions are deliberate and visible
Safety circuits do not rely on HMI navigation
Keep safety validation records with the project documentation.
Produce documentation that can be maintained
A compact combined PLC and HMI unit can reduce panel space, but it should not reduce documentation quality. The next technician needs to understand what was installed and why.
Maintain a project file that includes:
Electrical drawings
I/O schedule
PLC program backup
HMI project backup
Parameter list
Analogue scaling records
Communication settings
Fault list
Commissioning notes
Software versions and passwords managed under site policy
Use meaningful PLC tag names and comments. Group logic by function, such as infeed, clamp, fill, discharge and faults. Keep HMI object names clear enough that a later change can be made without hunting through anonymous buttons and indicators.
If setpoints are adjustable from the HMI, record normal ranges and access levels. Not every adjustment should be open to every user. By the same token, do not hide basic recovery information behind a password that operators cannot access during a stoppage.
Commission in stages, not in one big switch-on
Commissioning should prove the machine progressively. A staged approach keeps faults easier to find and reduces risk.
A typical sequence looks like this:
Check wiring against drawings.
Verify power supplies and earthing.
Test each input on the HMI and in the PLC.
Test each output with loads isolated where practical.
Confirm analogue readings and scaling.
Test communications with connected devices.
Run manual functions.
Step through the automatic sequence slowly.
Test faults, stops and recovery actions.
10. Record changes made during commissioning.
Do not skip fault testing. A machine that runs well once may still fail poorly when air pressure drops, a sensor misses a part or a drive trips.
Operator training should happen before handover, not after the first production problem. Walk through normal operation, manual mode, fault messages, reset rules and what not to bypass.
Choose Coolmay hardware from the finished scope
Coolmay combined HMI and PLC models can be a good fit where a machine needs a compact controller with local operator interface. The best model depends on the finished scope, not just the screen size.
Match the selected unit to:
Total digital inputs and outputs
Relay or transistor output needs
Analogue input and output requirements
Communication ports and supported protocols
Required screen size and HMI layout
Environmental conditions
Panel space and wiring access
Spare I/O for future changes
If several machines are being upgraded across a site or across multiple Australian locations, standardising on a small set of models can simplify spares and support. Still, each machine should have its own signal schedule and sequence description. Similar machines often contain small differences that matter.
For current automation options and Coolmay-related hardware support, refer to the ProSense automation range when comparing controller requirements against available products.
A good upgrade makes the machine easier to understand
A control upgrade should leave the machine clearer than it was before. The operator should know why it will not start. Maintenance should know which sensor, output or condition caused the stop. The next programmer should be able to follow the logic without reverse-engineering every rung or screen object.
Start with the sequence. Build the signal schedule. Match the I/O to the real devices. Confirm analogue and communication details. Write fault messages that explain the problem. Keep the documentation with the machine.
That approach turns a combined PLC and HMI upgrade from a hardware swap into a control system that can be operated, maintained and improved with confidence.
