How to maintain a PLC (Programmable Logic Controller)
As many of us know, PLCs (programmable logic controllers) are staples in the factory automation world. In order to have them running optimally and as efficiently as possible, routine maintenance is imperative. Generally, manufacturers produce PLCs to endure strenuous, unsterilized environments. By adhering to an adequate maintenance schedule, PLCs operating timeframe can be lengthened.
Protect your PLC
Always be on the lookout for corrosive and conductive contaminants that have the potential to become a detriment to a PLCs’ components. By completing visual inspections for black dust and blowing airborne particles from the PLC’s vicinity, you are lowering the likelihood of contamination.
Is power flowing?
A PLC will not operate correctly without adequate power. To avoid any operation bugs, remain vigilant of any surges or shorts.
Calibrate Analog Components
Always refer to the preventative maintenance schedule for any analog input device. Analog inputs need to be cleaned regularly and calibrated as accurately as possible.
Take EMI into consideration
EMI (electromagnetic interference) is known to cause horrible issues for PLCs without clearly indicating what the specific issue is or how to go about fixing it. To remain ahead of the game, many perform an audit of the local wiring to pinpoint potential EMI sources before they interfere with the operation of your PLC. Lower-level components and high-current wires often interfere with each other, which wiring designs must take into consideration.
Additional PLC Maintenance Tips
By creating a PLC maintenance checklist and adhering to it strictly, operating errors can likely be avoided. The space between the PLC and the machine it’s controlling should be minimal.
MRO Electric and Supply has new and refurbished Modicon PLC parts available here. We also offer repair pricing. For more information, please call 800-691-8511 or email email@example.com.
FANUC Alarm keys: These keys are located on the machine panel that displays alarm intelligence for the machine panel. MRO Electric has several FANUC part numbers starting with A06B, A20B, and A16B in-stock. These keys differ from the alarm keys correlated with the control panel.
FANUC Auto key: This is the key on the CNC machine (including the A16B, A17B & A20B product line) that reshapes the operation mode to automatic. Automatic mode authorizes an operator to contact and execute a part program stored in memory. Automatic mode is called memory mode on some FANUC CNC controls at times.
A safety function that determines if the tool has moved beyond its set boundaries. Forbidden zones can be programmed to specify areas where the tool can and cannot enter.
Page keys: The up and down arrow keys located on the MDI keypad (A20B ) that allow an operator to move through various screens and fields one page at a time.
Parentheses: ( ). Curved brackets used to separate program text information from CNC program commands.
Part program: A series of instructions used by a CNC machine to perform the necessary sequence of operations to machine a specific workpiece.
POS: A function key located on the MDI keypad that displays the position screen that shows axis locations.
Power off: The red button on a CNC control panel that shuts off power to the control.
Power on: The green button on a CNC control panel that provides power to the control.
PRGRM: A function key located on the MDI keypad that displays the program screen and blocks of the current part program.
Program edit keys: Keys located on the MDI keypad that allow an operator to alter, insert, or delete data from stored memory.
Program protect switch: A switch located on the machine control panel that allows the operator to secure current program information. The program protect switch prevents accidental or intentional deletion of programs in memory.
Program source keys: The group of keys on the operator panel that control how part programs are used. The AUTO, EDIT, and MDI keys that comprise the program source keys are distinct machine modes.
Rapid traverse: The movement of machine components at the fastest possible rate of travel. Rapid traverse motion merely requires an endpoint for the movement.
Reference position: A fixed position on a machine tool to which the tool can easily be moved by the reference position return function.
Reset key: A key located on the MDI keypad that stops all machine motion and places the program cursor at the top of the current program.
Shift key: A key located on the MDI keypad that allows an operator to access letters and special characters found on the address keys.
SINGL BLOCK key: A key that activates the single block feature on the GE FANUC 0-C control. The single block function runs the program one block at a time to prove out the program.
Soft keys: Keys located directly below the display screen that have different purposes depending on which function key has been chosen. The function of each soft key is visible on the display screen between brackets.
SP: A key that allows an operator to enter a space when manually entering data.
Spindle jog key: A key located on the machine panel that rotates the spindle incrementally in either a clockwise or counterclockwise direction.
Spindle keys: The area of the CNC machine control that allows the operator to manually control the rotation of the spindle in a clockwise or counter-clockwise direction. The spindle keys include CW (clockwise) and CCW (counter-clockwise), STOP, and JOG.
TEACH key: A key that changes the operation mode of a CNC machine to allow tool positions obtained by manual operation to be stored in memory.
Tool limit switch: The component that prevents a tool from exceeding the set direction limit on an axis. The tool limit switch detects overtravel.
Zero return key: Also known as the home key, zero return automatically moves the spindle to the machine zero position.
Auto mode: Auto mode is the mode that enables an operator to contact and execute a part program stored in the machine.
AUX/Graph: AUX/Graph is a function key located on the MDI keypad (A20B) that demonstrates the graphics screen.
Axis/direction keys: Axis/direction keys are located in the area of the machine control that enables an operator to select a specific axis.
BLOCK DELET key: BLOCK DELET key is a machine control that delivers the option of leaving out a predetermined series of program blocks. A block delete authorizes the operator to run two versions of the identical program.
Brackets: [ ]. Punctuation marks used to distinguish CNC program commands from macro statements.
CAN key: The CAN key is located on the MDI keypad that backspaces the cursor to remove the last character entered. It also drops any program block that is highlighted during a block edit.
Control Panel: The Control Panel is a group of controls on a CNC machine (A02B, A16B, A17B & A20B) that runs, store, and edits the commands of a part program and other coordinate details.
Coolant keys: Coolant Keys are the area of the CNC machine control that enables an operator to switch the coolant on and off, manually or automatically, during a program cycle.
Cursor keys: Cursor keys are the up and down arrow keys located on the MDI keypad that authorize an operator to move through numerous screens and fields in the control, edit and search for CNC programs, and move the cursor through the program or screen options.
Cycle start: Cycle start is the control button used to initiate a program or continue a program that has been previously stopped.
Cycle stop: The control button used to bring a program to a temporary halt. Also known as feed hold, cycle stop pauses tool feed but does not pause spindle movement.
DGNOS/PARAM: A function key located on the MDI keypad that demonstrates the diagnostics and parameters screens.
Display screen: The main screen of the machine that displays urgent information for the operator.
DRY RUN key: A key that activates the dry run feature on a CNC machine (example: . The dry run function checks a program quickly without cutting parts.
EDIT key: The key on the CNC machine that modifies the operation mode to edit. Edit mode allows an operator to make changes to a part program and store those changes.
EDIT mode: The mode that enables an operator to modify a part program and store those changes.
Emergency stop: Used for emergencies only, the control button that automatically shuts down all machine functions.
End-of-block key: EOB. A signal that marks the end of a part program block. An end-of-block signal is symbolized by a semicolon (;) in a part program.
Execution keys: The area of the CNC machine control that enables an operator to begin or end a part program. The execution keys include CYCLE START and CYCLE STOP.
Feed hold: The control button used to pause a program. Also known as cycle stop, feed hold pauses tool feed but does not stop spindle movement.
Function keys: Keys located on the MDI keypad that allows the operator to choose between contrasting tasks.
HOME key: A key that automatically moves the spindle to the machine zero position. The HOME key is called the zero return key on some machines at times.
Input buffer: A temporary location on a computer that holds all incoming information before it continues to the CPU for processing.
Input key: A key located on the MDI keypad that enables an operator to enter data into the input buffer. This key is also used to input data from an input/output unit.
Jog feed: In JOG mode, the continuous movement of a tool in a direction along a selected axis.
JOG key: The area of the machine control that allows an operator to move a selected axis. Jog keys are often called axis direction keys.
Machine function keys: The area of the control panel that allows an operator to perform different functions depending on what display or mode is selected. The machine function keys include SINGL BLOCK, BLOCK DELET, and DRY RUN.
Machine panel: The group of controls on a CNC machine that allow an operator to control machine components manually. Sometimes called the operator panel.
Machine zero: The position located at the farthest possible distance in a positive direction along the machine axes. Machine zero is permanently set for each particular CNC machine.
Manual data input keypad: The MDI keypad is located on the control panel and houses the address, numeric, and navigation keys.
Manual pulse generator: A circular handwheel on a CNC machine that can move a tool incrementally along an axis. On some machines, the MPG is known as the “handle.”
Manual pulse generator keys: Keys located on the machine panel that allow the operator to move the tool incrementally along an axis.
MDI key: The key on the CNC machine that changes the operation mode to manual data input mode. Manual data input mode lets an operator enter and execute program data without disturbing stored data.
MDI mode: An operation mode that lets an operator enter and execute program data without disturbing stored data.
MPG keys: The keys on the operator panel that control the size of incremental movement of the manual pulse generator.
No. key: A key that allows an operator to enter a numerical value into the input buffer. The SHIFT key must be used with the No. key.
Numeric keys: Keys located on the MDI keypad that allow an operator to enter numbers, a minus sign, and a decimal point into the control. These keys also contain the CAN key, manual JOG arrow keys, the EOB key, the BLOCK DELET, and the right and left cursor move keys.
Offset register: Area of the machine control that holds tool geometry, wear, and work offset settings.
OFSET: A function key located on the MDI keypad that displays tool offsets and settings.
OFSET MESUR key: A key on the CNC machine control panel that allows the operator to determine and set a tool offset. It measures the current coordinate value and the coordinate value of a command, and uses the difference as the offset value. If the offset value is already known, pressing the OFSET MESUR key moves the tool to the specified offset position.
Operation keys: The keys located on the operator panel that allow an operator to move tools and set offsets.
Operation mode keys: The AUTO, EDIT, and MDI keys that change the operation mode of the CNC machine.
Operator panel: The group of controls on a CNC machine that allow an operator to control machine components manually. Sometimes called the machine panel.
OPR/ALARM: A function key located on the MDI keypad that displays the alarm screen.
Output/start key: A key located on the MDI keypad that allows an operator to start an automatic operation and output data into an input/output unit.
Override: A machine control component that adjusts programmed values such as speed and feed rate by a certain percentage during operation.
Over-travel check: A safety function that determines if the tool has moved beyond its set boundaries. Forbidden zones can be programmed to specify areas where the tool can and cannot enter.
AC or DC Drives Comparison: Which is best for you?
An AC drive stands for Alternating Current, but could also be referred to as an adjustable speed drive, adjustable frequency drive, variable frequency drive, variable speed drive, frequency converter, inverters and a power converter. Typically, they are used to control the speed of an electric motor in order to enhance the operation of numerous applications relying on electric motors, minimize mechanical stress on motor control applications, generate energy as efficiently as possible, cut down on energy usage and, lastly, optimize process control.
Also known as adjustable speed drives, inverters and power converters, adjustable frequency drives, and variable speed drives, AC drives are similar to DC drives because an AC input is regulated to DC by simple bridge rectifiers, commonly referred to as SCRs. Because AC drives use a capacitor bank to stabilize and smooth this DC voltage, the DC output would be half cycle according to AC input phase frequency. Then, power is supplied to the motor in the output section of the drive by means of 6 output transistor or IGBT modules. Essentially, the AC input current is converted by the drive to DC and, again, converted back to AC in order to supply the motor. The current is converted twice by the drive because the AC input is either 50 or 60-hertz cycles. When the DC voltage is converted to AC again by the drive, it uses a carrier frequency of at least 2 KHZ to 100 KHZ in more complex drives. Therefore, the output current is able to be raised tens or hundreds of times without burning up the motor coil.
The AC motor is also able to rapidly switch speeds with zero problems because of this function. AC drives typically have numerous types of feedbacks from simple, 2-line incremental encoders, to resolvers or absolute encoders with a significant resolution that facilitates the drive to calculate motor shaft speed and angle as spot-on as possible. There is a third circuit called regeneration on a handful of larger, more powerful drives. This circuit converts the inertia of the load and motor to AC power and transfers it back to the input lines when the motor transitions from a significantly high speed to a low one, which, in the long run, would conserve on power and increase energy efficiency.
AC drives serve many different industrial and commercial applications.
Essentially, a DC drive converts an AC drive into direct current, otherwise known as DC to operate a DC motor. The majority of DC drives use a handful of thyristors (also known as SCR’s) to craft a half cycle of DC output from a single phase AC input, also known as the half-bridge method. The more complex ones use up to 6 SCR’s to power a DC output from a 3 phase AC input, which is known as the full-bridge. Therefore, in the full-bridge method, we have 2 SCR’s for every input phase. The aspects of a DC drive are as follows: compact in size, outstanding speed regulation, broad speed range, cost-effective for medium and high HP applications, and speed changes that are derived from by increasing or decreasing the amount of DC voltage the drive feeds the motor.
Controlled by the gate input, an SCR switch is similar to a one direction switch and turns on by applying a low voltage to the gates. The drive can control the motor speed by applying the voltage to the gate at a contrasting angle of the input phase. To authenticate the motor speed and compensate if necessary, the majority of DC drives require the motor to have a tachometer as means of feedback. A tachometer is essentially a mini permanent magnet DC motor accompanied by the main motor’s shaft.
Because higher motor speed generates more voltage in the tachometer, the drive references this voltage to ensure the motor is operating at a correct speed per-user settings. More compact DC motors have a permanent magnet field while larger DC motors have a separate coil inside the motor, also known as a field, which eliminates the need for a permanent magnet in the motor. DC drives with field output typically have a more compact circuit to supply the field coil. DC drives are best used in when a DC motor exists in a safe and dry atmosphere and the use of DPG, DPG-FV, TENV, or TEFC motor enclosures is required, motor speeds are able to reach 2500 RPM, application requirements are medium or large, and starting torque is either unpredictable or greater than 150%.
DC drives are commonly considered problematic, despite their prestige for having simple circuits, providing high start-up torque, and being ideal for applications with constant speed due to the requirement of commutators and brush assemblies in their motors. These motors can become worn over time, have operational issues, and will likely require labor to preserve.
On the opposite side of the spectrum, AC drives are considered more energy-friendly and are able to endure rapid speed changes more efficiently due to their running induction motors. Often times, they have hundreds of numerous programmable parameters for secure protection. Although, because of these factors, the AC drive is more complex, modernized software is simplifying their overall use.
In previous years, DC drives were regularly utilized due to their simplicity, the majority of machine manufacturers prefer to use AC drives as of late. The complexity of an AC drive has been repeatedly simplified and fine-tuned, resulting in a plethora of advantages.
Though in the past DC drives were often utilized due to their simplicity, most machine manufacturers now prefer to use AC drives (especially for servo applications). The intricacy of an AC drive has been simplified over time and has many upper hands.
Control Techniques Commander CDE Trips: Troubleshooting
When a failure occurs with the CDE drive the display will flash a series of segment characters for the trip.
Example: tr iP OU
Commander CDE series stores the past ten failure codes in parameters #10.14 – 10.23 in trip number form. A numeric value trip code is a basic form of the symptom for the technician to work with. These past trips can be accessed via the keypad by entering the value of 149 in the keypad at parameter 00.
Scroll to menu 10, for parameter #10.14 to see a trip number.
Symptom explanations provide an avenue on how to analyze the drive for particular problems.
To make the troubleshooting process easier a chart was created to link the type of trip with the symptom.
The Unidrive SP can be enabled to run in several ways. The drive can use digital inputs, keypad, or a field buss networks to give the OK to run. The drive will display inh, rdy, or run depending on the given commands. The drive can be programmed to use positive or negative logic. The logic type is set up at #8.29 in the Control Techniques Unidrive SP. The Unidrive SP defaults to positive logic. When the drive is in positive logic you will need to inject +24VDC to activate the digital inputs. The +24VDC can be supplied by the drive or externally.
The Unidrive SP can be enabled to run in numerous ways.
When the drive is in the terminal mode the following sequence occurs under default conditions:
Inh = Drive disabled = Connect pins 22-31 drive should go to rdy
Rdy = Drive enabled = Connect pins 22-26 drive should go to run
Run = Drive is enabled and ready to run when a speed reference is applied
Parameter #0.05 sets up the Reference Select. This will tell the drive where to search for run commands and speed references. You will only need to close the enable signal if it is set to pad. Then, the keypad can be used to control the drive and to set the speed reference. The speed reference will come in on an analog input if you choose a terminal code. The digital inputs will select the enable, run, and preset selections. The drive should operate as seen above if the digital inputs are activated correctly.
When the drive is not running, there are several additional parameters in menu 6 that can assess the issue. The digital inputs may be configured wrong or inactive if the parameters are not going to a 1 with the corresponding commands. Check the following parameters:
#6.15 = 1 = Drive enabled
#6.43 = 1 = Control word disabled, Set to 1 for Field Buss Control
#6.29 = 1 = Hardware Enable (Pin 31 is activated)
#6.30 = 1 = Run Forward #6.31 = 1 = Jog
#6.32 = 1 = Run Reverse
#6.33 = 1 = Forward/Reverse
#6.34 = 1 = Run
#6.37 = 1 = Jog Reverse
#6.39 = 1 = Not Stop
The voltage on the corresponding digital inputs should be measured if the parameters in menu 6 aren’t changing state accordingly. The DC voltage should change between 0VDC and 24VDC when a command is given. Check the digital input configuration in menu 8 if menu 6 isn’t changing and the voltage is.
To control the start/stop functions, the drive does not have to use the digital inputs. When #6.43 = 1 the control word is enabled. The drive will now accept a decimal value from 0 to 32767 at #6.42. This decimal value can be converted to a binary value.To see the function that will be carried out, you can reference the binary value to the chart below.
The drive still may not run if the digital inputs and the drive sequencer are each working properly. There could be an issue with the speed reference to the drive if the display shows Run but the motor isn’t turning. The speed reference is able to be applied in several methods. An analog input can be used (current or voltage), preset speeds, and a field buss reference. The example is a 0-10VDC signal on analog input #1.
The final speed of the demand is parameter #3.01. The speed reference should be displayed here if the digital inputs and the drive sequencer are failing to operate properly. Check menu 1 and 2 to determine where it is stopping if the reference is not getting to this point.
If the drive is running in torque mode, the torque reference will come on parameter #4.08 under default conditions. #4.08 is able to be linked to an analog input or be written to via a filed buss network.
#7.01 should be inspected to determine if it changes with the change in reference at terminal 5 once the signal has been confirmed. #7.01 goes from +/- 0% – 100%. Check the destination of the speed reference at #7.10 if everything looks good. Follow it to the destination and confirm the speed reference value is arriving there and then through #3.01.
Contact the America’s Service Center if the drive will still not run after the Speed Reference, Digital Inputs and Drive Sequencer have all been confirmed.
MRO Electric and Supply has new and refurbished Control Techniques Unidrives available now, and also offers repair pricing. For more information, please call 800-691-8511 or email firstname.lastname@example.org.
HF Faults are not recorded in the Drive Historical Fault Log
All of the above HF trips in BLUE are typically a result of some sort of hardware failure on the UD90A control PCB. This control board is common to all Unidrive Classics.
For the HF codes in RED refer to the following page
HF82 Large option module missing
If one of the UD7x large option modules is removed, the trip may be expected. There is an issue with either the large option module or the UD90A control PCB if this trip occurs at any other time than the case above.
HF83 Power Board Code Failure
Because the UD90A control PCB was unable to recognize the power rating of the power PCB it is connected to, this trip occurred.
The trip is likely due to the power PCB in the Drive or a problem with the UD90A control PCB on Unidrive Sizes 1 to 4 (which includes UNI1401, UNI1402, UNI1403, UNI1404, UNI1405, UNI2401, UNI2402, UNI2403, UNI3401, UNI3402, UNI3403, UNI3404, UINI3405, UNI4401, UNI4402, UNI4403, and UNI4404).
UD99 PCB or the UD90A PCB cause the trip on a Unidrive Size 5. The interconnects between the PCBs should also be checked, as they could also cause a trip.
HF84 Current Offset Trim Failure
Due to an issue with the current feedback on the drive, this trip occurs. The trip is likely due to the power PCB in the Drive on Unidrive Sizes 1 to 4. An issue with the UD90A control PCB may also cause this trip.
The UD99 PCB or the UD90A PCB cause the trip on a Unidrive Size 5, along with the interconnects between the PCBs.
HF88 Watchdog Failure
This trip can result from a faulty UD7x Co-Processor. With power off, remove Co-Processor and re-apply power.
HF82 Large option module missing
If one of the UD7x larger option modules is removed while the Drive is powered up, this trip is likely to occur. There is an issue with either the UD90A control PCB or the large option module if this trip were to occur at any other time.
HF83 Power Board Code Failure
The UD90A control PCB was unable to recognize the power rating of the power PCB it is connected to, which is what caused the trip.
The trip is likely due to the power PCB in the Drive on Unidrive Sizes 1 to 4, however, an issue with the UD90A control PCB is also able to cause this trip.
The trip is caused by the UD90A PCB, the UD99 PCB, or the interconnects between the PCBs on a Unidrive Size 5.
HF84 Current Offset Trim Failure
If there is an issue with the current feedback on the Drive, this trip will occur. The trip is likely due to the power PCB in the Drive, but an issue with the UD90A control PCB could also result in a trip on Unidrive Sizes 1 to 4.
On a Unidrive Size 5, the trip is cause by either UD99 PCB or the UD90A PCB. The interconnects between the PCBs could also cause this trip and should be checked.
A trip could be caused by either UD99 PCB, UD90A PCB, or the interconnects between the PCBs on a Unidrive Size 5.
HF88 Watchdog Failure
A faulty UD7x Co-Processor and large option module, ( includes UD70, UD71, UD73, UD74, UD75, and UD76) can cause this trip. Remove Co-Processor and re-apply power with power off.