Mitsubishi Q68ADIELS Current Analog Input Module

Only for current input (4-20mA / 0-20mA), 8 channels, AI module dedicated to MELSEC-Q series; comparison within the same series: Q68ADV is the 8-channel voltage input module, and Q64AD is the 4-channel module with switchable voltage/current input.

Core Specifications

Model: Q68ADI

Channels: 8CH, current input only, voltage signal input is not supported

Input range: DC 0～20mA (4～20mA transmitters are widely used)

Input resistance: 250Ω (built-in sampling resistor; do NOT add an extra 250Ω resistor externally)

Occupied I/O points: 16 points

5VDC backplane power consumption: 0.64A

Conversion speed: 80μs per channel; an additional 160μs total conversion time is required when temperature drift compensation is enabled

Accuracy: ±0.1%FS at 25±5℃; ±0.3%FS with temperature drift compensation, ±0.4%FS without compensation

Resolution modes (selected by software)

Normal mode: -4096～+4095 (0~20mA full scale corresponds to 0~4000)

High-resolution mode: -12288～+12287 (0~20mA full scale corresponds to 0~12000)

Maximum allowable input current: ±30mA (permanent damage may occur if exceeded)

Isolation: Optocoupler isolation between module terminals and PLC power supply; no isolation between channels (crosstalk may occur when multiple transmitters share the same ground)

Withstand voltage: AC500V for 1 minute (terminal side vs PLC power supply side)

Dimensions: 27.4(W) × 98(H) × 90(D) mm; Weight: 0.19kg

Certifications: CE, UL/cUL, UKCA; marine certifications ABS/BV/DNV, etc.

📌 Model Code Explanation

Q: MELSEC-Q series PLC

68: 8-channel analog

A: Analog

D: Digital (A/D conversion)

I: Input, I = Current (V = Voltage for Q68ADV)

🧩 Software Configuration

Configuration software: GX Works2 / GX Developer + GX Configurator-AD (dedicated analog configuration tool, recommended to reduce heavy FROM/TO instruction programming)

Configurable items: Channel enable/disable, range (0~20mA), resolution mode, temperature drift compensation, moving average filtering, offset & gain calibration

Data storage: Raw A/D converted values are stored in the module buffer memory (BFM); the PLC reads data via FROM instructions

Common 4-20mA Conversion (High-resolution mode, 0~12000)

4mA → 2400

20mA → 12000

Span: 9600 (corresponds to 16mA)

Engineering conversion formula: Engineering value = (Raw value 2400) / 9600 × (Upper range limit − Lower range limit) + Lower range limit

🔌 Wiring Guidelines (Common Pitfalls)

1. 2-wire transmitter (most common): Transmitter positive to module I+, transmitter negative to module I−; transmitters are powered by external 24VDC. The module does NOT supply power to transmitters.
2. 4-wire transmitter: Connect the two signal current wires to I+/I− of the corresponding channel; power supply is independently wired to 24VDC.
3. No inter-channel isolation: For multi-signal applications, single-point grounding on the transmitter side is recommended to avoid ground loops and unstable readings.
4. Shielded cable: The shield of analog cable shall be grounded at one end only (ground at transmitter side, floating at PLC side).
5. Prohibition: Do not connect an extra 250Ω resistor in parallel externally. The built-in 250Ω resistor will cause abnormal readings after parallel connection.

⚠️ Replacement & Selection Comparison

Replacement reminder: Q68ADI cannot directly replace Q68ADV. One is for current and the other for voltage, with completely different internal circuits.

🛠️ Common Troubleshooting

1. Fixed reading at 0: No power supply to transmitter, broken wire, or channel disabled in software
2. Fluctuating and unstable readings: Ground loop interference, shield grounded at both ends, cables routed together with power cables, inter-channel crosstalk
3. Reading stuck at full scale: Short-circuited signal wire, faulty transmitter, input current exceeding 20mA
4. Severe drift at low/high temperature: Temperature drift compensation function not enabled
5. Module ERR light on: Incorrect buffer memory parameter settings, wrong FROM/TO read/write addresses, poor contact between module and base unit

Application Scenarios of Mitsubishi Q68ADI (For 4-20mA/0-20mA Current Transmitters, 8-Channel AI for Q Series)

Matched with SHAKO solenoid valve pneumatic circuits mentioned previously: Q68ADI collects process values such as pressure and flow; the PLC executes PID/logic calculation and drives SD90822DJSN coils via output points to control PU520/BM520 pneumatic valves, forming closed-loop pneumatic regulation systems.

Scenario 1: Pneumatic Automation Circuits (Most common with SHAKO solenoid valves)

Collected signals: Main air supply pipe pressure, branch pipe pressure, vacuum negative pressure, filter differential pressure, air receiver tank pressure (4-20mA pressure transmitters)

Control logic: Open air inlet solenoid valve when pressure is below lower limit; open pressure relief valve for overpressure; PID constant pressure regulation

Typical equipment: Transfer machines, tooling fixtures, welding jigs, vacuum adsorption equipment, valve island systems

Features: Mostly 2-wire pressure transmitters which perfectly match Q68ADI; 8 channels support simultaneous multi-point pressure acquisition and centralized monitoring

Scenario 2: Packaging Machinery (Horizontal flow wrappers, vertical form-fill-seal machines, heat sealers)

Collected signals: Heat sealing temperature (4-20mA temperature transmitter), hopper level, air supply pressure, film tension, ink tank liquid level

Interlock control: Pneumatic cutting cylinders, pressure rollers, material stop solenoid valves (SHAKO PU520) interlocked by temperature and pressure values

Advantages: Fast conversion speed of 80μs per channel suitable for high-frequency, short-cycle packaging processes; standardized wiring with universal 4-20mA 2-wire transmitters

Scenario 3: Water Treatment, RO Reverse Osmosis & Dosing Systems

Collected signals: Liquid level (submersible level transmitter), flow (electromagnetic/vortex flowmeter), PH/ORP transmitter, turbidity, chemical dosing flow, pre-membrane and post-membrane differential pressure

Interlock control: On-off control for inlet, concentrate and dosing pneumatic/electric valves, flow totalization, high/low liquid level interlock protection

Working condition: Current loop is preferred in humid sites for better anti-interference performance than voltage signals; Q68ADI is suitable for multi-point process acquisition

Scenario 4: Extrusion, Injection Molding & Rubber and Plastic Auxiliary Machines (Material loaders, pelletizers, extrusion lines)

Collected signals: Melt pressure, barrel temperature, oil temperature, vacuum feeding negative pressure, hopper level, cooling water flow

Control logic: Interlock feeding pneumatic valves and blow cleaning solenoid valves based on negative pressure and pressure; alarm and shutdown on overpressure

Working condition: Stable long-distance transmission of current signals in high-temperature and dusty workshops

Scenario 5: 3C Non-Standard Automation, Testing Machines and Assembly Equipment

Collected signals: Press-fitting force (4-20mA force sensor), test air pressure, leak detection differential pressure, fixture clamping pressure

Functions: Press-fitting force monitoring, air tightness leak judgment, OK/NG sorting; pressure curve recording and MES data upload

Description: Transmitters are centrally arranged in clean workshops. The high-density 8-channel design saves slot space. Double-solenoid valves are used to maintain station status.

Scenario 6: HVAC, Clean Rooms, Fan Coils and Purification Air Conditioning

Collected signals: Duct differential pressure, static pressure, temperature & humidity transmitter, water flow, temperature difference between inlet and outlet of chiller

Control logic: Pneumatic damper actuators and chilled water circuit regulating valves, constant static pressure, constant temperature & humidity PID regulation

Scenario 7: Material Conveying, Sorting Lines and Warehouse Conveying Lines

Collected signals: Belt weigher flow, silo level, dust removal negative pressure, air supply pressure

Interlock logic: Trigger feeding/discharging pneumatic valves by high/low level; alarm when dust removal negative pressure is insufficient

Scenario 8: Small-Scale Chemical Industry, Fluid Proportioning & Quantitative Dosing Systems

Collected signals: Flow transmitter, tank liquid level, medium pressure

Functions: Flow totalization, quantitative feeding, proportion control, over-limit interlock shutoff; suitable for multi-component batching with simultaneous multi-channel flow collection

Scenario 9: Pump Stations, Air Compressor Rooms and Centralized Air Supply Station Monitoring

Collected signals: Air compressor discharge pressure, air receiver pressure, pipeline flow, cooling water temperature, filter differential pressure

Functions: Load/unload linkage of multiple air compressors, overpressure protection, pressure logging, alarm upload to SCADA

Selection Guidelines (When to prefer Q68ADI and when to avoid it)

Suitable applications:

All measuring points use 4-20mA 2-wire / 4-wire transmitters (pressure, level, flow, temperature, force, PH)

8-channel current acquisition required, high channel density on a single module and cost-sensitive

Long signal transmission distance or sites with heavy electromagnetic interference (current loop has better anti-interference performance than voltage signals)

Unsuitable (avoid selection):

0~10V, ±5V voltage signal acquisition required → Select Q68ADV

Electrical isolation between channels required (chemical explosion-proof, high interference sites) → Select isolated Q68AD-G

Flexible switching between voltage and current per channel for scattered measuring points → Select Q64AD

Mitsubishi Current Analog Input (AI) Module List

Two categories: 【Current-only modules for 4~20mA / 0~20mA】, 【Dual-purpose voltage/current modules with current range selectable by software】, sorted by MELSEC-Q / iQ-R / L / FX (iQ-F) series

1. MELSEC-Q Series (Q68ADI included)

Current-only Modules (Current input only, voltage not supported)

Dual-purpose Voltage/Current Modules (Range switchable by software for current acquisition)

There is no Q64ADI (4-channel current-only module) for Q series; Q68ADI is the only 8-channel current-only option.

1. MELSEC iQ-R Series (New-generation RCPU)

Current-only Modules

Dual-purpose Voltage/Current Modules (Current range selectable)

| R60AD4 | 4CH | Voltage/current selectable | Screw terminal general model |

| R60ADH4 | 4CH | High-speed voltage/current | 1μs/ch high-speed sampling |

| R60AD8-G | 8CH | Isolated voltage/current | 40-pin |

| R60AD16-G | 16CH | Isolated voltage/current | High-density 16 channels |

III. MELSEC-L Series (LCPU)

No dedicated current-only modules for L series; all modules support both voltage and current

| L60AD4 | 4CH | Switchable voltage / current |

| L60AD8 | 8CH | Switchable voltage / current |

| L60AD16 | 16CH | Switchable voltage / current |

| L60AD4-G | 4CH | Isolated voltage / current |

| L60MD4-G | 4CH | Multi-function (voltage/current/RTD/TC) |

1. FX / iQ-F (FX5U, FX3U) Compact PLC Analog Adapters

FX series uses ADP adapters instead of backplane modules; all dual-purpose voltage/current

| FX5-4AD-ADP | 4CH | FX5U dedicated, supports 4-20mA |

| FX3U-4AD-ADP | 4CH | FX3U, supports 4-20mA |

| FX3UC-4AD | 4CH | Module type for FX3UC |

| FX2N-8AD | 8CH | Old FX2N (discontinued) |

1. Quick Selection Reference (For procurement & replacement)
2. Q68ADI (Q) ↔ R60ADI8 (R): Equivalent function, 8-channel current-only
3. HART smart transmitters required → R60ADI8-HA (iQ-R)
4. Heavy interference, chemical or explosion-proof cabinet with channel isolation requirement: Q68AD-G (Q dual-purpose) / R60ADI8-HA, R60AD6-DG (R isolated current-only)
5. Small quantity of 4 measuring points requiring flexible voltage/current switching: Q64AD / R60AD4
6. Critical Notes to Avoid Mistakes

Q68ADI supports current only and cannot collect 0~10V voltage signals; Q68ADV supports voltage only

For dual-purpose modules (Q64AD, R60AD4), the current mode must be selected in software parameters for correct 4-20mA acquisition

All Mitsubishi current AI modules have built-in 250Ω sampling resistors, never connect an extra 250Ω resistor externally