Description
Product Introduction
Let me address the model number first—you asked about IC694ALG728, but the documented module is IC695ALG728. The “695” prefix indicates it’s part of the newer RX3i series, while “694” modules are typically older generation. This unit is essentially the HART-enabled version of the standard 8-channel analog output module.I’ve deployed these in chemical plants where you need to talk to smart transmitters while controlling valves. The GE IC695ALG728 gives you eight configurable output channels plus HART communication—four channels can communicate with HART devices simultaneously. That means you can read secondary variables from smart positioners or transmitters while sending 4-20mA control signals. The 8ms update rate keeps control loops tight, though HART communication adds about 6-8 seconds per channel when active.
Key Technical Specifications
| Parameter | Value |
|---|---|
| Output Channels | 8 non-isolated |
| Output Ranges | ±10 VDC, 0-10 VDC, 0-20 mA, 4-20 mA |
| Resolution | Voltage: 14.9 bits; Current: 15.9 bits (0-20mA), 15.6 bits (4-20mA) |
| Update Rate | 8 ms (all channels without HART), 16 ms (with HART enabled) |
| HART Protocol | Version 5.0, supports 4 channels simultaneously |
| Accuracy @ 25°C | ±0.15% of full scale |
| Accuracy @ 60°C | ±0.30% of full scale |
| Output Settling Time | Voltage: 2 ms; Current: 23 ms (70 ms with HART) |
| Maximum Load | Current: 850Ω @ 20V; Voltage: ≥1kΩ |
| External Power | 19.2-30.0 VDC, 250 mA typical |
| Backplane Power | 375 mA @ +3.3 VDC |
| Isolation | 2500 VDC optical (field to backplane) |
| Dimensions | 34 × 145 × 140 mm |
GE IC695ALG728
Quality Control Process (SOP Transparency)
Testing HART modules requires both analog output verification and digital communication validation.
- Incoming Verification: Serial validation against Emerson’s database, visual inspection of the 20-pin removable terminal block. We check for the HART modem indicator LEDs—four green LEDs should be present for HART channels.
- Analog Output Test: Using an RX3i test rack with CPU315, we run output tests across all eight channels. A Fluke 725 calibrator measures output accuracy at 0%, 25%, 50%, 75%, and 100% for all four signal ranges. We verify the module stays within ±0.15% FS at room temperature.
- HART Communication Test: We connect a Rosemount 3051S pressure transmitter to one of the first four channels. Using Proficy Machine Edition, we verify the module can read the transmitter’s secondary variables (PV, SV, TV, QV) via HART commands. We test all four HART-capable channels sequentially.
- Load and Settling Time Test: We apply maximum specified loads (850Ω for current, 1kΩ for voltage) and measure settling time with an oscilloscope. Voltage outputs must settle within 2ms, current outputs within 23ms for step changes.
- Final QC & Packaging: QC inspector signs off, terminal screws torqued to 0.6 N·m, module sealed in anti-static bag with desiccant, placed in custom foam. QC label shows “HART functionality verified on channels 1-4.”
Replacement Pitfall Guide (Field Engineer’s Warnings)
HART adds complexity—here’s where engineers get tripped up.
- ❗ Only Four Channels Support HART: Channels 1-4 support HART communication; channels 5-8 are standard analog outputs only. Don’t wire a HART device to channel 7 expecting communication—it won’t work. I’ve seen entire control strategies fail because someone wired smart valves to the wrong channels.
- ❗ HART Slows Update Rates Dramatically: When HART is active on a channel, update time jumps from 8ms to about 6-8 seconds per poll. This matters for fast control loops. Use HART only for configuration and occasional diagnostics, not for primary control data.
- ❗ External 24VDC Power is Critical: This module draws 250mA from the external 24VDC supply—more than non-HART modules. Undersize your power supply and HART communication will fail intermittently. Calculate total system load with 20% margin.
- ❗ Grounding and Noise are HART Killers: HART signals are low-level (1mA p-p) superimposed on 4-20mA. Poor grounding or electrical noise from VFDs can corrupt communication. Use twisted-pair shielded cable, ground at one end only, and keep away from power cables.
- ❗ Configuration Software Matters: You need Proficy Machine Edition v8.0 or later for full HART functionality. Older versions might not recognize all HART device descriptors. Check compatibility before attempting field upgrades.
Keep these five points in mind and you’ll eliminate roughly 90% of rework.
