Description
Product Introduction & Engineering Value
Delivering eight software-configurable analog voltage command signals from a single 1746 slot, the Allen-Bradley 1746-NO8V maximizes rack density in space-constrained control cabinets. It feeds ±10V DC drive reference commands and 0–10V actuator signals directly to field units with sub-millisecond loop updates.
Facilities running mature SLC 500 architecture depend on this module to keep multi-axis motion and throttle valves running without expanding rack backplanes. The high resolution eliminates output signal stepping in delicate closed-loop applications.
Technical Specifications
| Specification | Parameter Value |
| Output Channels | 8 single-ended voltage channels |
| Voltage Output Ranges | ±10V DC, 0 to 10V DC, 0 to 5V DC, 1 to 5V DC |
| D/A Resolution | 16-bit (305 µV/LSB at ±10V range) |
| Output Conversion Time | 1 ms for all 8 channels |
| Backplane Current (5V DC) | 120 mA |
| Backplane Current (24V DC) | 250 mA max (drawn from external 24V DC bus) |
| External Power Requirement | 20.4 to 26.4V DC at 175 mA min |
| Channel-to-Backplane Isolation | 500V DC continuous |
| Maximum Load Capacitance | 1 µF maximum |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
Field Application & The “Trench” Experience
When a high-speed packaging plant suffered an intermittent voltage signal dropout on a multi-lane carton former, six servo drives started losing position alignment simultaneously. A technician traced the fault to a degraded output driver on an old 4-channel card. Replacing it with a 1746-NO8V allowed the plant to reassign all drive speed references to a single module, eliminating inter-slot backplane delay and restoring perfect line synchronization.
- Automotive Stamping Line Lubrication: Commanding eight independent proportional flow control valves across multi-die stamping presses.
- HVAC Multi-Zone VFD Cascade: Sending 0–10V DC speed reference signals to variable frequency drives on eight fresh air intake fans.
- Turbine Bypass Valve Control: Driving electro-hydraulic servo valves on steam turbine bypass systems requiring precise ±10V DC control.
- 1746-NO8V
- 1746-NO8V
Transparency SOP: QA & Testing
- Terminal & PCB Inspection: Checking edge connector fingers, terminal block retention, and inspecting onboard bypass capacitors for signs of thermal aging.
- External Power Bus Stressing: Validating external 24V DC power rail regulation across the operating voltage range (20.4V to 26.4V DC).
- 8-Channel Voltage Verification: Sending full-scale digital word values (-32,768 to +32,767) in RSLogix 500 and verifying exact voltage outputs on a 6.5-digit bench multimeter across all eight channels.
- Capacitive Load & Burn-In Test: Running full ±10V output sweeps across simulated cable capacitive loads in a burn-in test chamber for 12 hours.
The Veteran’s Tech Trap Guide
- ⚠️ External 24V DC Mandatory Connection: The 1746-NO8V will not generate output voltages using backplane power alone. You must connect a dedicated 24V DC field supply to terminals 11 (+24V) and 12 (24V Common) on the terminal block. Leaving these unpowered results in 0V across all channels despite valid status lights.
- PRO TIP: Common Mode Voltage Limits: Because output commons are tied internally, all eight voltage loops share a common ground reference. If your driven field devices (like non-isolated VFD analog inputs) have differing ground potentials, ground loop currents will corrupt your 0-10V command signals. Use signal isolators when driving drives with ungrounded control circuits.
- ⚠️ Short Circuit Limitations: While outputs feature current-limiting protection against temporary shorts to common, prolonged accidental shorts to external voltage rails will damage the onboard operational amplifiers.
Dynamic FAQ
Q: Can I configure channels for different voltage ranges on the same 1746-NO8V?
A: Yes. Output voltage ranges are set per channel via output data word configurations in your RSLogix 500 program file, allowing you to mix 0–10V and ±10V ranges on a single card.
Q: Does the 1746- use the same wiring harness as the 1746-NO4V?
A: No. Due to the higher channel count, the terminal layout is different. You must update your field wiring to match the 1746- pinout assignment.
Q: What happens to the outputs if the SLC CPU enters Rem Prog mode or faults?
A: Output state behavior during processor faults or program mode transitions depends on your module configuration word settings—you can select hold last state or reset to 0V.
Q: Are these replacement cards tested before shipping?
A: Every card undergoes full hardware inspection, external supply voltage verification, and multi-point calibration testing on an active SLC 500 rack.
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