New MITSUBISHI Module Q64AD

Mitsubishi Q64AD | MELSEC-Q Series 4-Channel Analog-to-Digital Converter Module — Voltage and Current Input, 16-Bit Resolution, 80µs/Channel, EEPROM, Built-in Isolation

Part Number: Q64AD

Manufacturer: Mitsubishi Electric Corporation (Japan)

Product Line: MELSEC-Q Series — Analog I/O Modules

LED Indicators: RUN (normal/watch dog error), ERROR (error status)

Configuration Tool: GX Configurator-AD (or GX Works2 intelligent function module tool)

Compatible CPUs: All MELSEC-Q CPU modules operating in Q mode

Status: Active product (MELSEC-Q platform)

Applications: Process variable acquisition, flow and pressure measurement, temperature transmitter input, PID control, inverter speed feedback, multi-sensor data logging

Overview

The Mitsubishi Q64AD sits in the MELSEC-Q platform's analog module lineup as the general-purpose, high-resolution, four-channel A/D converter — the module that covers the standard industrial signal ranges (both voltage and current, across all commonly used spans) in a single compact slot.

For process control applications, condition monitoring, and closed-loop feedback systems built on the Q-series PLC, the Q64AD provides the analog input infrastructure that the CPU's program requires to work with real-world measured variables.

The MELSEC-Q's slot-based backplane architecture means adding analog input capability is a matter of selecting a slot, inserting the module, and configuring it through the engineering software.

There is no separate power supply to wire, no DIN rail position to negotiate, and no communication cable to run — the module takes the backplane's 5V logic supply for its internal circuits and draws 24V DC from the terminal block for the analog portion.

The Q64AD's 27.4mm slot width keeps it narrow enough that a fully populated 12-slot Q-series base unit can hold a substantial mix of analog and digital modules without the panel becoming unmanageably large.

What engineers working with process sensors care about most is signal integrity and repeatability — that the digital value the CPU reads actually corresponds to the physical measurement, day after day, without drift from ambient temperature changes or power-up/power-down cycles.

The Q64AD addresses this directly: its 16-bit conversion resolution provides 65,536 quantisation levels across each input range (for instance, approximately 0.30mV per count on the ±10V range), its EEPROM stores the calibrated offset and gain values non-volatilely so they survive power cycling without battery backup, and its photocoupler isolation between the input terminals and the backplane bus prevents ground loop currents from corrupting the measurement.

Key Specifications

Input Range Selection — Per-Channel Configuration

Each of the Q64AD's four channels can be assigned its own input range independently of the other channels.

A machine installation might connect a ±10V pressure transmitter to channel 1, a 4–20mA flow sensor to channel 2, a 0–10V position feedback to channel 3, and a 1–5V temperature transmitter to channel 4 — all simultaneously active in their respective ranges from the same module.

The range assignment is made in the intelligent function module switch settings in GX Developer or GX Works2. Once configured, the module's internal range registers store the setting and apply the correct conversion characteristic for each channel.

The I/O conversion characteristic is a straight line through the offset value (the analog input value that produces a digital output of 0) and the gain value (the analog input value that produces the maximum digital output).

Both values are adjustable to trim the conversion for the specific sensor's actual output characteristics — a factory calibration that accounts for sensor-to-sensor variation without requiring the Q64AD itself to be adjusted.

The EEPROM storage ensures that calibration data set during commissioning persists without battery backup.

On power-up, the Q64AD reads its stored offset and gain values from EEPROM and begins converting immediately with the calibrated characteristics — a practical benefit for installations where battery replacement schedules are difficult to maintain, or where the module may be powered down and restarted repeatedly during machine maintenance.

Conversion Speed and Averaging

At 80 µs per active channel, the Q64AD converts rapidly — a full four-channel scan completes in 320 µs, refreshing all four buffer memory values before the typical Q-series CPU scan cycle ends.

This speed allows the Q64AD to track relatively fast process variables in real time and feed the CPU program with current measurements each scan.

For applications where the analog signal contains electrical noise that produces visible measurement jitter — sensor cables running near high-power equipment, unshielded cables near VFDs, or inherently noisy signal sources — the Q64AD's digital averaging function smooths the reported value.

Averaging can be set for each channel individually, selecting either time-based averaging (averaging over a specified number of milliseconds) or count-based averaging (averaging over a specified number of conversions).

The averaged value is what the CPU reads from the buffer memory; the module continues converting at 80 µs internally and accumulates samples for the average calculation. This removes noise without slowing the fundamental conversion hardware.

Buffer Memory Interface — How the CPU Reads Converted Values

The Q64AD communicates with the CPU through buffer memory — a dedicated memory area inside the module accessed by the CPU using the FROM/TO instructions (or the intelligent function module direct access device in GX Works2 structured programs).

The key buffer memory areas are: CH□ digital output value (the current A/D conversion result for each channel), CH□ averaging enable/disable, CH□ offset/gain values, and error status registers.

The CPU reads the channel's converted digital value from its buffer memory address in the ladder program, typically storing it in a data register for further processing — scaling to engineering units, comparison with setpoints, use in PID loops, or logging to a data recorder.

The conversion happens continuously inside the Q64AD regardless of whether the CPU is reading the buffer memory or not; the buffer memory simply holds the most recently completed conversion result until it is overwritten by the next conversion.

FAQ

Q1: The Q64AD occupies 16 I/O points. Does this affect the Q-series CPU's available discrete I/O count?

Yes. Intelligent function modules like the Q64AD occupy a defined number of I/O points in the CPU's I/O map, even though they are not discrete input or output modules.

The 16-point allocation is used for the module's own data exchange signals — operating condition signals and control signals — but these 16 points do not correspond to physical input or output terminals. 

The actual analog converted values are read via FROM instructions accessing the module's buffer memory, not via the I/O map.

The 16 I/O point allocation must be accounted for in the system's total I/O point count, as each Q-series base unit has a defined maximum I/O point capacity.

Q2: What happens if the input voltage exceeds the maximum rated ±15V — will the module be damaged?

The Q64AD's input circuits include protection against input voltages up to ±15V for voltage inputs and ±30mA for current inputs.

Signals within these limits will not damage the module. Signals that briefly exceed these limits — transients from cable disconnection, ground faults, or nearby switching equipment — may cause conversion errors during the transient event but should not damage the hardware if the exceedance is brief and within the absolute maximum ratings. 

Sustained voltages significantly above these levels, or direct connection of mains AC to the input terminals, would damage the input circuits.

The photocoupler isolation protects the backplane and CPU from damage even if the analog input circuitry is compromised.

Q3: Can the Q64AD module be calibrated in the field, and how is this done?

The Q64AD's offset and gain values can be adjusted in the field through the intelligent function module switch settings and the offset/gain setting mode supported by GX Configurator-AD.

In offset/gain setting mode (activated via buffer memory write), the engineer applies known reference voltages or currents to the input terminal and writes the corresponding target digital value to the module — the module calculates the correction factor and stores it in EEPROM. 

This procedure allows the Q64AD's conversion to be matched to the specific characteristics of the connected sensors, correcting for sensor-to-sensor variation, cable voltage drop, or slight differences in the installation's reference voltage.

Q4: How many Q64AD modules can be installed in a single Q-series system?

The number of Q64AD modules is not hard-limited by the module type itself, but by the total I/O point capacity and the base unit slot count.

A standard Q-series system supports up to 64 slots across multiple base units connected via extension base cables. 

Each Q64AD occupies one slot (27.4mm wide) and 16 I/O points.

A system with 64 slots theoretically supports 64 Q64AD modules, providing 256 analog input channels — though in practice, system power budgets, base unit configurations, and the mix with other module types will determine the actual count.

Q5: Does the Q64AD support averaging per individual channel, or is averaging applied to all channels simultaneously?

Averaging is configurable per individual channel.

Each channel has its own averaging enable/disable and averaging setting in the buffer memory — channel 1 can have 50ms time-based averaging enabled while channel 2 runs with no averaging, channel 3 uses count-based averaging of 10 samples, and channel 4 is also unaveraged. 

This per-channel independence allows the module to be optimised for each signal's characteristics without compromising the responsiveness of faster-changing channels.