Omron C500 PLC Installation and Maintenance Guide

Omron C500 PLC Installation and Maintenance Guide

System Overview and Applicable Scenarios

Omron C500 is a classic rack mounted programmable controller widely used in industrial automation systems from the late 1980s to the 1990s. Although it has been replaced by new models, there are still a large number of equipment in operation in a large number of old production lines, ship control systems, and infrastructure projects. Mastering the hardware installation, power configuration, I/O unit selection, and maintenance methods of C500 has high practical value for ensuring the stable operation of existing systems and rapid fault repair.

The C500 adopts a modular rack structure, consisting of a CPU rack and up to three expansion I/O racks, with a total of 512 I/O points. Its core components include: backplane, power unit, CPU unit, I/O unit (input/output), special function unit (such as analog, high-speed counting, position control), communication unit (Host Link, PC Link, SYSMAC NET Link), and remote I/O unit. This article is based on the official hardware installation manual and provides a complete set of operation guidelines for common needs of on-site engineers.

System composition and model identification

2.1 Backplane

C500 has multiple backplane models for installing CPU, power supply, and I/O units. The backplane provides I/O slots from left to right, with the rightmost slot typically used for power units, and some backplane rightmost slots also support link units.

Backboard model, I/O slot number, link slot location, applicable scenarios

C500-BC091 has a maximum configuration of 9 I/O slots and 5 link slots, requiring a large amount of I/O

3G2A5-BC081 8 I/O slots 3 link slots Conventional CPU rack

C500-BC082 requires multiple link units for 8 I/O slots and 5 link slots

C500-BC061 6 I/O slots 5 link slots Medium configuration

3G2A5-BC051 5 I/O slots 3 link slots Compact CPU rack

C500-BC052 5 I/O slots 5 link slots Link unit priority

C500-BC031 Minimum configuration of 3 I/O slots and 3 link slots

The expansion I/O rack uses dedicated backplanes: 3G2A5-BI081 (8 slots) and 3G2A5-BI051 (5 slots), which require separate configuration of power and I/O interface units.

2.2 CPU Unit

The C500 CPU model is C500-CP11-V1, which does not come with a power supply and memory pack. It requires an additional power supply and memory pack (RAM or ROM). The front panel of the CPU provides:

Peripheral connector (direct insertion programmer)

Memory pack slot (located on the left side)

Run/Stop Switch

Status indicator lights (POWER, RUN, ALARM, BATT LOW)

2.3 Power Supply Unit

The power unit is installed on the far right side of the rack (some of the rightmost slots on the backplane also allow for the installation of link units, and the power supply needs to be installed in another dedicated location). The power supply provides 5V DC to all units on the backplane, and some models also provide 24V DC service power.

Model Input Voltage 5V Output Capacity Can be used for I/O Unit Current 24V DC Output

3G2A5-PS221-E 100-120/200-240V AC (switchable) 7A 5A 0.8A

3G2A5-PS223-E 24V DC 12A 10A None

C500-PS213-E 24V DC 9A 5A None

3G2A5-PS222-E 100-120/200-240V AC 7A 6.5A 0.8A (for expansion rack)

3G2A5-PS212-E 24V DC 7A 6.5A None

Key point: The nominal output capacity of the power unit is different from the actual current available for the I/O unit. For example, PS221-E outputs 7A, but 2A has already been consumed by the CPU and backplane itself, and only 5A is actually available for the I/O unit. When designing the system, the 5V current consumption of all I/O units, special units, and link units installed on the same rack must be added up and not exceed the "available current" of the rack power supply.

2.4 I/O Control Unit and I/O Interface Unit

I/O control unit (3G2A5-II101): must be installed on the leftmost side (first I/O slot) of the CPU rack for connecting to the expansion I/O rack. Even without expansion, it can still be installed (retaining future expansion capabilities).

I/O Interface Unit (3G2A5-II002): Each expansion I/O rack must have an I/O interface unit installed in its leftmost I/O slot for communication with the I/O control unit of the CPU rack.

Installation environment requirements

The C500 PLC must be installed in a control cabinet that meets the following conditions, otherwise it may cause malfunctions or shorten its lifespan:

Parameter requirements

Operating at an ambient temperature of 0-55 ℃ and storing at -20~65 ℃

Humidity 35%~85% RH, no condensation

Altitude ≤ 2000m

Pollution without corrosive gases, conductive dust, metal powder

Vibration of 10~55Hz, double amplitude of 0.5mm (direct installation); 16.7Hz， Double amplitude 1mm (DIN rail installation)

Impact 10G, 3 times in the downward direction

The installation direction is vertical, and the text can be read normally. The CPU rack is located above, and the expansion rack is located below

Rack spacing of 70-120mm, convenient for heat dissipation and wiring

The total length of the extension cable between each rack is ≤ 12m, and the length of a single cable is ≤ 2m

Heat dissipation design:

Maintain sufficient clearance between racks (≥ 70mm).

If the ambient temperature inside the control cabinet may exceed 55 ℃, a cooling fan must be installed to ensure that the air inlet and outlet are unobstructed.

Avoid installing the PLC directly above heating equipment (such as high-power transformers), and the distance should be greater than 150mm.

Anti static:

In environments with low humidity, the human body may carry static electricity. Before touching the PLC, first touch a grounded metal object (such as a plumbing pipe) to release static electricity.

During installation, prevent conductive foreign objects such as metal shavings and wire ends from falling into the interior of the casing.

Power selection and current consumption calculation

This is the most error prone step in C500 installation. The power unit of each rack (CPU rack and each expansion rack) must be able to provide sufficient 5V current to all units on the same rack.

4.1 5V current consumption of commonly used I/O units (excerpt)

Input unit:

Model type, point count, 5V consumption (mA)

3G2A5-ID112 DC 5-12V 16 10

3G2A5-ID213 DC 12-24V 16 20

3G2A5-ID215 DC 12-24V slow speed 32 160

3G2A5-ID218 DC 12-24V Fast 32 160

3G2A5-ID212 DC 24V Dynamic 64 300

3G2A5-ID219 DC 24V Static 64 700

3G2A5-IA121 AC 100-120V 16 10

3G2A5-IA222 AC 200-240V 16 12

3G2A5-IM211 AC/DC 12-24V 16 10

Output unit:

Model type, point count, 5V consumption (mA)

3G2A5-OC221 Relay 16 100

3G2A5-OC223 relay independent common terminal 16 100

3G2A5-OC224 relay 32 200

3G2A5-OD411 transistor 1A 16 160

3G2A5-OD412 transistor 0.3A 32 230

C500-OD212 transistor PNP 32 230

3G2A5-OD213 transistor dynamic 64 460 (+5mA x ON point)

3G2A5-OA121 bidirectional thyristor 16 300

3G2A5-OA222 bidirectional thyristor 16 300

C500-OA226 bidirectional thyristor 16 450

Special Unit (Example):

Model Description 5V Consumption (mA)

3G2A5-AD001~005 A/D 2-channel 300

3G2A5-AD006/007 A/D 4-channel 750

C500-AD101 A/D 8-channel 880

3G2A5-DA001~005 D/A 2-channel 550

3G2A5-CT001/012 high-speed counter 330/550

3G2A5-PID01-E PID 1400

3G2A5-NC103-E Position Control 1 Axis 1400

C500-LK009-V1 PC Link 900

C500-SNT31-V4 SYSMAC NET Link 1400

Calculation example:

A CPU rack is equipped with a PS221-E power supply (capable of 5V and 5A current). Installation on the rack: CPU unit (approximately 2A), I/O control unit (approximately 0.3A), one ID218 (0.16A), one OD411 (0.16A), one OA222 (0.3A), one ID212 (0.3A), and one high-precision CT012 (0.55A). Sum=2.77A, less than 5A, feasible.

Note: The PS222-E of the expansion rack has a usable current of 6.5A, which is higher than the power supply of the CPU rack.

I/O Unit Wiring Specification

5.1 Terminals and crimping terminals

The C500 I/O unit uses M3.5 screw terminals, and it is recommended to use crimp terminals. It is forbidden to directly screw bare wires under the screw. The dimensions of the crimping terminals are as follows:

Applicable wire: AWG22-14 (0.3~2.0mm ²)

Screw tightening torque: 8 kg · cm (approximately 0.78 N · m), maximum not exceeding this value

Important: Each unit is equipped with a detachable terminal block. Loosen the installation screws on both sides of the terminal block to remove the entire terminal block. This is very convenient for unit replacement or maintenance, without the need to disconnect the wires.

5.2 Precautions for wiring input units

DC input: Pay attention to polarity. For world standard input units, the COM terminal can be connected to positive or negative, corresponding to Sink or Source inputs.

AC input: If using a reed switch as the input contact, it is necessary to ensure that the rated current of the contact is ≥ 1A, otherwise surge current may cause contact welding.

Two wire sensors (such as photoelectric switches and proximity switches): there is leakage current. If the leakage current is greater than 1.3mA, it may be mistakenly connected when the input is in the OFF state. Solution: Connect a bleeder resistor in parallel at the input end. Calculation formula:

Maximum resistance value R [k Ω]=7.2/(2.4 × I2 leak [mA] -3)

Minimum power W=2.3/R

Input signal pulse width: The response time of the DC input unit is usually 1.5ms (15ms for slow type). If the input pulse width is less than the scanning period, the signal may be lost. It should be solved through programming or adjusting the input filtering time.

5.3 Precautions for output unit wiring

Relay output (OC221/223/224):

Maximum switch capacity: 2A at 250V AC or 24V DC (resistive load)

Inductive loads (such as contactors and solenoid valves) generate reverse electromotive force, and surge absorbers (AC circuit: RC absorption) must be connected in parallel at both ends of the load; DC circuit: freewheeling diode)

Relay lifespan: 300000 cycles under resistive load and 100000 cycles under inductive load; Mechanical lifespan of 50 million cycles

Every 8 output points share the same common terminal, and the total current must not exceed the allowable value of the common terminal (8A)

Transistor output (OD series):

Switching voltage: 12~48V DC

Residual voltage: approximately 1.4-1.5V (TTL output is 0.4V)

Leakage current: ≤ 0.1mA

Response time: 0.2ms (ON), 0.3ms (OFF)

When driving inductive loads, a freewheeling diode must be added

When driving loads with high surge currents such as incandescent lamps, the surge current can reach 10 times the rated current, and a current limiting circuit (such as connecting a resistor in series at the output end or using a buffer circuit) needs to be added

Bidirectional thyristor output (OA series):

Switching voltage: up to 250V AC

Leakage current: 3~6mA, may cause slight illumination of extremely small loads (such as LED lights), and parallel discharge resistors are required

Response time: 1ms (ON), turn off time is 1/2 cycle of the load frequency

Each unit is equipped with two built-in fuses (5A 250V), which can be replaced

5.4 Wiring Separation Principle

I/O signal lines are strictly prohibited from being laid in the same cable tray as high-voltage power lines (>400V 10A or>220V 20A). If parallel wiring is necessary, the spacing should be ≥ 300mm, and a metal partition with intermediate grounding should be used.

The use of shielded twisted pair cables (AWG14) can effectively reduce noise.

It is recommended that the length of the I/O cable should not exceed 10m (special units have separate regulations).

The expansion I/O connection cable (flat cable between CPU rack and expansion rack) must not be in the same slot as the power line.

Expansion cable length: Choose a model that is 20cm longer than the actual distance between the two racks. Standard lengths include 30cm, 50cm, 80cm, 1m, and 2m. The maximum length of a single piece is 2m.

Expand configuration rules

C500 can connect up to 3 expansion I/O racks. The configuration steps are as follows:

CPU rack: Install power supply, CPU unit, and I/O control unit (leftmost I/O slot).

Expansion rack 1: Install the power supply and I/O interface unit (leftmost I/O slot), and then install the I/O unit as needed.

Expansion racks 2 and 3 also require their own power supply and I/O interface units.

Connect the I/O control unit to the first I/O interface unit using an I/O connection cable, and then connect the first interface unit to the second interface unit in series.

Limitations:

The total number of I/O points for all racks shall not exceed 512 points.

Special units, link units, remote I/O master stations, etc. can be installed in CPU racks or expansion racks, but it should be noted that some units can only be installed in specific slots (such as Host Link units that can only be installed in the link slots of the CPU rack or directly on the CPU).

The maximum number of PC Link units is 2, and they can only be installed in the rightmost slots of the CPU rack (different backplane regulations apply).

SYSMAC NET Link unit and Host Link unit cannot be installed simultaneously.

Memory package installation and battery maintenance

7.1 Memory Package Types

The C500 CPU does not have a built-in program storage area and must insert a memory pack.

RAM package: Models 3G2A5-MR431 (16K words), 3G2A5-MR831 (24K words). The data is held by the battery on the CPU backplane (power-off hold). Can read and write online, suitable for debugging stage.

ROM package: Model 3G2A5-MP831 (maximum 24K characters). EPROM chips (2764/27128, etc.) are required to write the program into the chip and insert it. Data is not lost during power outages, but cannot be modified online.

7.2 EPROM chip installation

There are three IC sockets (CHIP0, CHIP1, CHIP2) on the ROM package. Set the jumper according to the required capacity and insert the corresponding chip:

Memory Capacity Jumper Setting CHIP0 CHIP1 CHIP2

8K bytes 128 2764--

16K bytes 128 2764 2764-

24K bytes 128 2764 2764 2764

16K bytes (27128) 128 27128--

24K bytes (27128+2764) 128 27128 2764-

7.3 Memory Package Installation Steps

Power outage: It must be operated with the PLC power turned off.

Use a screwdriver to pry open the memory pack cover on the left side of the CPU front panel (press the buckle inward and push it upwards).

Insert the memory pack (with the component facing left) into the slot and push it evenly to the bottom (there may be slight resistance, indicating that the connector is engaged).

Cover the lid back.

7.4 Battery replacement

The RAM package relies on the internal lithium battery of the CPU to maintain data. When the battery voltage is too low, the ALARM indicator light on the front panel of the CPU flashes and the programmer screen displays "BATT LOW". At this point, the battery should be replaced within a week, otherwise the data will be lost.

Battery model: 3G2A9-BAT08 (lithium battery)

Replacement steps (must be completed within 5 minutes):

If the PLC has been powered off, power on for at least 1 minute and then turn off the power.

Open the battery compartment cover (usually located in the upper right or front of the CPU).

Unplug the old battery connector and immediately insert the new battery.

Cover the compartment lid.

After powering on again, if "BATT LOW" still appears, press the CLR, FUN, MONTR keys on the programmer or power on again to clear the message.

Battery life: Approximately 4 years in a 25 ℃ environment. The higher the temperature, the shorter the lifespan.

Grounding and noise prevention

8.1 Grounding Requirements

Use AWG14 (≥ 2mm ²) copper wire with a grounding resistance of<100 Ω.

The length of the grounding wire should be as short as possible (not exceeding 20m).

The GR terminal (protective grounding) must be grounded. LG terminals (wire grounded) are usually not grounded. If there is severe noise, LG can be short circuited to GR and grounded.

The grounding of PLC must be independent and cannot share the grounding electrode with power equipment (motor, frequency converter), nor can it be connected to building structural metal parts.

All GR terminals of the racks (CPU and expansion rack) should be connected to the same grounding point.

8.2 Noise Suppression Measures

Maintain a distance of at least 300mm between the I/O signal line and the power line.

Use shielded twisted pair cables, with the shielding layer grounded at one end.

For AC inductive loads (contactor coils), parallel RC absorption circuits (typical values: resistance 50 Ω, capacitance 0.47 μ F, withstand voltage 200V) are connected at both ends of the load.

For DC inductive loads, parallel freewheeling diodes (diode withstand voltage ≥ 3 times the load voltage, average current ≥ 1A).

If there are multiple PLCs or frequency converters in the control cabinet, power filters should be installed.

Common fault diagnosis and troubleshooting

9.1 Meaning of LED indicator lights

LED color normal status abnormal meaning

POWER green is always on but not lit: no power supply or internal fuse broken

RUN green constantly on: CPU not running (program error or manual STOP)

ALARM red not flashing: low battery voltage; Always on: CPU hardware failure or memory error

BATT LOW red not shining: low battery voltage

9.2 Common faults and solutions

Possible causes and solutions for the phenomenon

The POWER light is not on and there is no input power supply; Measure the voltage at the power terminal when the internal fuse is blown; Replace the fuse (PS221/222/223 with 3A 250V)

RUN light not on, ALARM light flashing, program syntax error; END instruction is missing and the programmer check is incorrect; Clear errors and rerun

ALARM light constantly on, CPU hardware failure; Poor contact of memory package, power off and reinsert memory package; If it still doesn't work, replace the CPU

BATT LOW light on, battery voltage low, replace battery within one week

The input signal is correct but the PLC does not respond. The response time is set too long; Wiring error check input filtering time (DIP switch or programming); Check the wiring of the S/S terminal

The output point does not operate and the fuse is blown (relay/thyristor output); Check the fuse of the output unit for damage (such as using 5A 250V for OD411/OD217); Replace unit

The expansion rack I/O is not working, and the I/O control unit or I/O interface unit is not installed; Check if II101 and II002 are installed for loose connection cables; Re plug and unplug the connecting cable and lock it securely

When programming, it prompts "I/O VERITY ERROR". The configuration of the I/O unit does not match the actual situation; Check the I/O unit model and slot position for memory packet faults; Reinstall the memory package

9.3 Fuse replacement

Power fuse (located on the side of the power unit, circular knob):

Use a Phillips screwdriver to rotate counterclockwise by about 50 ° and remove the fuse holder.

Replace the fuse with the same specifications (3A 250V for PS22x, 4A 125V for PS213).

Rotate clockwise.

Output unit fuses (such as OD411, OA121, etc.):

The output unit needs to be removed (power off first, remove the terminal block, remove the fixing screws, and pull out the unit).

Open the casing and locate the fuse (usually a 5mm x 20mm glass tube) on the circuit board.

Replace and assemble.