SNAP PAC System Architecture and Selection Guide

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: