SNAP PAC System Architecture and Selection Guide

SNAP PAC System: An Ideal Platform for Industrial Automation and Control Integration

In the field of modern industrial automation, the flexibility, scalability, and reliability of control systems are key factors determining the success of projects. The SNAP PAC system launched by Opto 22 has been widely used in remote monitoring, data acquisition, and industrial control scenarios since its first release in 2007, thanks to its highly integrated hardware and software architecture. This article will provide a comprehensive and in-depth technical analysis of the SNAP PAC system from multiple dimensions, including system architecture, core components, network configuration, I/O module selection, and installation points.

System Overview and Architecture Design

The SNAP PAC system is a highly integrated automation platform, mainly composed of the following three parts:

PAC Project software suite: provides control programming based on flowcharts, HMI development and runtime environment, as well as optional OPC servers, database connection software, and PC based controllers.

SNAP PAC controller: including standalone or rack mounted industrial controllers, supporting RESTful APIs and multiple network protocols.

SNAP I/O modules: covering analog, digital, and serial communication modules, used to connect field devices, sensors, and actuators.

These three parts together form a system capable of handling everything from basic equipment monitoring to complete factory automation. It is worth noting that starting from 2022, due to the discontinuation of some key components, some SNAP PAC components are no longer produced. The document explicitly recommends the use of alternative components, such as replacing the discontinued EB series brain modules with R series controllers.

System Architecture Example and Scalability

The architecture design of the SNAP PAC system is highly flexible, making it easy to implement from small standalone systems to large-scale distributed control systems.

Minimum System Example: Only one rack mounted controller, local I/O, and free PAC Project Basic software are required. The control program (strategy) is developed on a PC and downloaded to the controller for independent operation. The HMI interface is built through PAC Display and can be accessed using the built-in REST API for IIoT data access.

Small system example: Adding distributed I/O units on the basis of the minimum system. Each I/O unit can independently handle functions such as counting, locking, watchdog timer, thermocouple linearization, PID closed-loop control, etc. Even if communication with the main controller is interrupted, local functions can continue to operate.

System expansion method:

Increasing distributed I/O: By adding more I/O processors and modules, analog, digital, and serial modules can be mixed at any location.

Add HMI seats: For multi client access, it is recommended to use OptoOPCServer to efficiently handle communication loads.

Enhance network security and IIoT capabilities: By adding groov EPIC edge programmable industrial controllers, the system's user authentication, device firewall, data encryption, MQTT communication, and mobile HMI capabilities can be significantly improved.

Accessing enterprise databases: Groov EPIC can easily exchange data with local or cloud databases and software services.

Integrated third-party system: Supports Modbus/TCP, EtherNet/IP, DF1 protocol, and provides RESTful API for developers to access tag data in the controller using any programming language.

Detailed explanation of core component selection

1. Software selection

The SNAP PAC system offers two versions of software suites:

PAC Project Basic (free): includes PAC Control (control programming), PAC Display (HMI development), and PAC Manager (configuration and diagnostics). Suitable for most standard monitoring applications.

PAC Project Professional (paid): adds OptoOPCServer (OPC 2.0 communication), OptoDataLink (ODBC database connection), and SoftPAC (PC based software controller) on the basis of Basic. In addition, Ethernet link redundancy and controller redundancy are also supported (note: controller redundancy function is no longer supported for new projects, and related hardware has been discontinued).

2. Controller selection

SNAP PAC R series (rack mounted): directly installed on the I/O rack, integrating I/O processing and control functions. The R1 model supports high-speed digital function, while the R2 model does not have high-speed digital function. Suitable for unit control or small-scale distributed systems. Support RESTful API.

SNAP PAC S series (standalone): With stronger performance, it can run up to 64 PAC Control flowcharts simultaneously (32 for R series). S1 provides 1 RS-485 and 2 RS-232 serial ports; S2 provides four software configurable serial ports for RS-232 or RS-485. Support communication with legacy Mistic serial I/O units (requires PAC Project Professional).

SoftPAC (PC based): A software controller running in the Windows environment, suitable for scenarios that require large amounts of file storage, mathematical calculations, or running multiple flowcharts simultaneously. Only supports Ethernet communication and does not support serial I/O units.

3. Selection of I/O processors (brain)

The document clearly states that all SNAP PAC EB and SB series brain modules have been discontinued since 2022. Opto 22 recommends using SNAP PAC R1 or R2 controllers as an alternative to I/O processors. These controllers can handle analog, digital, and serial I/O modules, and have built-in PID control (up to 96 loops), Modbus/TCP, SNMP, SMTP, and FTP functions.

Important difference: The R series controller is equipped with two independent Ethernet interfaces (each with its own IP address), while the two interfaces of the old EB brain are switched (sharing the same IP address and supporting daisy chain connections). Therefore, replacing EB with R series will not be able to achieve daisy chain topology.

4. Selection of I/O modules

The SNAP PAC system provides an extremely rich selection of I/O modules:

Digital input module:

Supports voltage type (5V, 24V, 125V) and dry contact type inputs.

Some modules support high-speed counting up to 20kHz (such as SNAP-IDC5 FAST).

High density modules such as SNAP-IDC-32 provide 32 input points, divided into 4 groups, each with 8 points sharing a common terminal.

Digital output module:

Including AC output (SNAP-OAC5), DC output (SNAP-ODC5SRC/SNK), reed relay output (SNAP-ODC5R), and mechanical power relay output (SNAP-OMR6-C).

The total current of a single module does not exceed 3A, and any channel can carry up to 3A.

The mechanical power relay module (OMR6-C) has C-type contacts, 6A switching capability, and built-in transient suppression (OMR6T-C).

Analog input module:

Supports multiple signal types such as current (± 20mA), voltage (± 150mV to ± 100V), RTD, thermocouple, thermistor, load current, RMS, etc.

The typical resolution is ± 25000 counts (approximately 14.5 bits+sign bits).

Isolation modules (models ending in - i) provide inter channel isolation (250V continuous, 1500V transient).

Analog output module:

Including current output (4-20mA or 0-20mA) and voltage output (0-5V, 0-10V, ± 10V).

The resolution is 12 bits (4095 counts).

SNAP-AOVA-8 is a multifunctional 8-channel module that can be configured with multiple current/voltage output ranges.

Serial communication module:

SNAP-SCM-232: Port RS-232, maximum 115.2kbps.

SNAP-SCM-485-422：RS-485/422， Supports 2-wire or 4-wire modes.

SNAP-SCM-ST2: Pulse/Direction Output, suitable for stepper motor control.

SNAP-SCM-CAN2B: CAN bus interface, supporting 10-1000kbps.

Network configuration and communication capability

The SNAP PAC system is based on Ethernet and retains support for serial networks to adapt to different industrial environments.

Standard Ethernet usage:

S-series and R-series controllers must use Ethernet 1 interface for BootP/IP address allocation.

The two Ethernet interfaces of the controller are independent interfaces and cannot be bridged or switched.

Redundant network links:

By utilizing the dual independent Ethernet interfaces of the S series and R series controllers, combined with PAC Project Professional, network link redundancy can be achieved.

Each controller has two independent IP addresses and is connected to two separate networks. When one link fails, communication automatically switches to another.

Network isolation and security:

The control network can be physically or logically isolated from the enterprise network.

Recommend using Groov EPIC as a front-end device, utilizing its firewall VPN、 Encryption and other security features protect SNAP PAC control networks.

Modbus/TCP and EtherNet/IP communication:

All SNAP PAC controllers natively support Modbus/TCP and EtherNet/IP protocols.

Data can be exchanged with Allen Bradley PLCs (such as ControlLogix, CompactLogix) through the Scratch Pad area.

Serial network options:

The S-series controller can be connected to the discontinued SB series serial brain via RS-485.

Supports PPP remote communication through RS-232 connection to a modem.

Support communication with legacy Mistic serial I/O (such as B3000, B3000-BRS, Mistic bricks), requires PAC Project Professional.

Power supply and installation points

Main power supply:

The SNAP rack requires a 5 VDC power supply (5.0 to 5.2 VDC, recommended minimum 4A).

Recommend using SNAP-PS5 (120/240 VAC input) or SNAP-PS5-24DC (24 VDC input).

Equipping each rack with an independent local isolated power supply can reduce voltage drops and ground loops, and improve system redundancy.

Circuit power supply:

Some simulation modules, such as the SNAP-AIMA series, require a 24 VDC loop power supply.

Optional SNAP-PS24A (0.75A) or SNAP-PS24U (1.25A).

Power consumption calculation:

The document provides a detailed power consumption calculation worksheet. For example:

SNAP PAC R series controller: 1.2A

Non isolated 4-channel digital module: 0.05A/piece

Isolation simulation module (- i or iSRC): 0.2A/piece

High density digital module: power consumption needs to be calculated according to specific modules

The total power consumption shall not exceed the rated value of the power supply (4A for SNAP-PS5/PS5-24DC, 5A for SNAP-PS5U).

Isolation type and safety design

The SNAP I/O module provides multiple isolation methods to protect the control system from on-site signal interference:

Optocoupler isolation: All solid-state modules provide 4000V transient isolation to separate field signals from control logic.

Galvanic Isolation: Each channel of certain modules (especially analog modules with - i) is isolated from each other, and the resistance between any two channel terminals is measured to be infinite.

Transformer isolation: The simulation module adopts transformer isolation to prevent noise and misreading caused by grounding loop current. The typical isolation voltage is 1500V.

SNAP TEX installation accessories

To simplify on-site wiring, Opto 22 offers SNAP TEX series accessories:

Prefabricated cables: SNAP-TEX-CBO6 (odd pin connection), SNAP-TEX-CBE6 (even pin connection), SNAP-TEX-CBS6 (no internal connection), length 6 feet, wire gauge 18 AWG.

Distribution board: SNAP-TEX-32 (32 way spring terminal, no fuse), SNAP-TEX-FB16-H/L (16 way, with fuses and LED indicators at each point, discontinued).

High density distribution rack: SNAP-IDC-HDB (input), SNAP-ODC-HDB (output), SNAP-UDC-HDB (universal), all provide LED status indication at each point and zone fuses.

DIN rail installation kit: suitable for power supply, controller, and rack. Specific accessory numbers can be found in the table on page 45 of the document.

Environmental specifications and certification

SNAP PAC system components typically meet the following environmental requirements:

Working temperature: -20 ° C to 70 ° C (some modules such as SNAP-AIRTD-8U can reach up to 80 ° C)

Storage temperature: -40 ° C to 85 ° C

Humidity: 5% to 95%, no condensation

Certification: UL 508C, CSA C22.2, IEC 68-2-6 (Vibration), ATEX (Partial Modules) RoHS、DFARS、UKCA

Most SNAP modules come with a lifetime warranty, while some special modules (such as the MA series with diagnostic switches) come with a 30 month warranty.