Description
Note: Many products are not yet listed. Please contact us for more product information. Our supply channels are constantly expanding, and we currently have 20 stable shared supply channels. Please confirm the model, product, price, and all other necessary information with customer service before placing an order. We offer new, refurbished, and used products, and prices are adjusted according to the year of the item you require.
Key Technical Specifications
| Parameter | Value |
|---|---|
| User Memory | 2 MB (logic + data) |
| I/O Memory | 478 KB |
| Local Port | RS232 serial programming port |
| Non‑volatile Storage | CompactFlash slot (1784‑CF64 / CF128) |
| Max Digital I/O | 128,000 |
| Max Analog I/O | 4,000 |
| Max Tasks | 32 (1 continuous, 31 periodic/event) |
| Max Connections | 250 controller connections |
| Programming Software | RSLogix 5000 |
| Supported Networks | EtherNet/IP, ControlNet, DeviceNet, DH+, SynchLink (via comm modules) |
| Backplane Current | 1.2 A @ 5.1 V DC |
| Operating Temperature | 0 °C to +60 °C, non‑condensing |
| Battery | Lithium battery for RTC and RAM retention |
| Weight | 0.98 kg |
| Certification | CE, Class I Div 2 |
Product Introduction
The Allen‑Bradley 1756‑L61A is Series A ControlLogix 5561 processor. It is the base model of the L6x family, without built‑in Ethernet; all network communication depends on separate 1756 communication cards. The RS232 front port is used for direct programming and troubleshooting. A CompactFlash card stores project backup, firmware and recipe data. It supports motion control, add‑on instructions and mixed I/O across multiple ControlLogix racks. Series A is the early revision of the L61, followed by B revision.
1756-L61A
1756-L61A
1756-L61A
1756-L61A
1756-L61A
Application Scenarios & Field Experience
Many sites mix L61A and L61B revisions. Firmware compatibility must be checked before swapping; A-series cannot run the latest high firmware versions supported by B revision.
- Automotive assembly lines: Conveyor sequencing, robot handshake and axis motion control.
- Water & wastewater plants: Pump control, chemical dosing and analog PID loops.
- Food & beverage batch systems: Recipe management, valve sequencing and alarm handling.
- Oil & gas auxiliary skids: Remote I/O control via ControlNet or EtherNet/IP.
In my experience, a wastewater plant had a 1756‑L61A fail after battery leakage corrupted internal RAM. The technician loaded the backup project from CompactFlash into the replacement A‑series CPU, matched firmware revision, verified all scheduled I/O and PID loops, then restored automatic operation. They added a battery replacement schedule to prevent repeat failures.
Standard Operating Procedure (SOP) for Quality Control
- Visual & Origin Inspection: Check OEM label, serial number, front key switch, RS232 port, CF slot, status LEDs and backplane edge fingers. Check for battery leakage marks.
- Live Rig Testing: Install in 1756 chassis, power up, download RSLogix5000 project, verify task execution, CF read/write and RS232 programming connection.
- Firmware & Revision Verification: Record firmware FRN, confirm A‑revision compatibility with the existing project and I/O modules.
- ESD‑Safe Packaging: Protect edge connector, place in static shielding bag, foam padding, label for ESD handling.
Frequently Asked Questions (FAQ)
Q1: What is the difference between 1756‑L61A and 1756‑L61B? A: A is the early revision with limited maximum firmware. B supports newer firmware releases and some bug fixes. They are mechanically interchangeable, but firmware must be matched. Q2: What warranty applies to this Allen Bradley 1756‑L61A? A: We offer a 12‑month warranty. Warranty covers hardware defects under rated operating conditions. Damage from battery leakage, CF card corruption, firmware mismatch or overvoltage is excluded. Q3: Is this 1756‑L61A stocked? A: Legacy discontinued part, stock is limited. Confirm lead time before outage. L71 is the modern functional replacement. Q4: Can I use this CPU for redundant controller pairs? A: No, native ControlLogix redundancy requires specific redundant CPU pairs and redundancy modules; standard does not support redundancy. Q5: Can I hot‑swap this CPU while the chassis is powered? A: Hot swap is supported on 1756 chassis, but all control logic and I/O will drop. Lock out interlocks and stop the process before replacement.
