IC670ALG330 GE FANUC ANALOG OUTPUT CURRENT 8PT MODULE IC670ALG33O

GE Fanuc IC670ALG330 | Field Control 8-Channel 0–20mA Current-Source Analog Output Module — 16-Bit / 1.5ms / Open-Wire Alarm 

Eight 0–20mA Outputs with 16-Bit Precision

The IC670ALG330 is the 8-channel current-source analog output module for GE Fanuc's Field Control distributed I/O system. It provides eight independent 0–20mA current loop outputs, each configurable with independent scaling parameters set by the user. The Bus Interface Unit (BIU) delivers engineering-unit values to the module over the Field Control backplane; the IC670ALG330 scales each value according to its configured parameters and drives the corresponding current output.

At 16-bit resolution (0.3125 μA per count), the module resolves the 0–20mA span into 65,536 steps. For a channel commanding a flow control valve from 0 to 100% with 4–20mA, each count represents approximately 0.0002% of the control span. This resolution far exceeds what most field instruments can utilise, but it eliminates the module as a precision limitation — the resolution constraint is the field instrument itself.

The 1.5ms channel update time means all eight channels complete their output update cycle every 1.5ms — fast enough for real-time closed-loop control loops where output latency would otherwise affect control quality. The channel update is independent; each channel responds to new command values from the BIU at this rate.

Open-wire detection is standard. The module monitors each output channel's current. If the current loop is broken — the 4–20mA wiring to a field device is disconnected — the current falls below the minimum threshold (1.0–3.5mA depending on the configured open-wire threshold). The module reports an open-wire alarm to the BIU, which propagates the alarm status to the PLC programme for operator alerting.

Key Specifications

Hold-Last-State — Fail Behaviour on Communication Loss

The IC670ALG330 supports configurable hold-last-state behaviour. When the BIU resets, no output data is received within the timeout period, backplane power is lost, or the module's watchdog timer expires — the module holds its last commanded output values rather than defaulting all outputs to zero. This is critical for process applications where forcing all 8 analog outputs to zero simultaneously could cause unsafe process states, valve slamming, or equipment damage.

Note: on backplane power loss or watchdog expiration, the resolution of the held value reduces from 16-bit to 14-bit — the held output remains active but at slightly reduced precision.

FAQ

Q1: Can the IC670ALG330 output 4–20mA as well as 0–20mA?

Yes. The output hardware range is 0–20mA, but the user-configurable scaling can set the commanded engineering value range to correspond to a 4–20mA span. The module outputs 4mA for the configured low-end engineering value and 20mA for the high-end. An open-wire condition (disconnected loop) drives the output below 4mA, which the open-wire alarm detects. Field devices expecting 4–20mA see the correct signal through scaling configuration alone.

Q2: Does the IC670ALG330 require the IC670CHS002 I/O base?

Yes. The IC670 series Field Control modules mount onto I/O terminal blocks (bases) — the IC670CHS002 (or IC670CHS001) provides the module mounting interface, backplane connectivity, and the field wiring terminal strip. The module and base are ordered separately. Confirm the correct base variant for the installation environment.

Q3: What happens if the external 24V DC supply to the IC670ALG330 is lost while the BIU backplane power remains?

The module's output channels lose their current drive when the external 24V DC supply is absent — the 24V external supply powers the DAC output stages directly. The module itself may remain partially powered from the BIU backplane supply, allowing it to report a fault status. All analog output currents fall to zero (or to whatever the hold-last-state mechanism maintains at reduced resolution) when the external supply is absent.

Q4: How is factory calibration restored to the IC670ALG330?

The IC670ALG330 stores factory calibration data in its Flash memory. If field calibration is performed and subsequently found to be incorrect, a reset command issued through the BIU or programming software restores all channels to the factory calibration values stored in Flash. No external reference equipment is needed for the factory calibration restore operation.

Q5: Where is the IC670ALG330 sourced after discontinuation?

Through the GE Fanuc Field Control aftermarket — Emerson-related automation parts dealers, tested surplus suppliers, and repair centres. The IC670 Field Control series has a substantial installed base in process control and factory automation; aftermarket availability is generally good. Confirm the module revision and I/O base compatibility when ordering.