SSR-RACK08
Eight-Channel Solid-State Relay (OPTO22, Gordos) Mounting & Interface Rack

Functional description
The SSR-RACK08 is a mounting and interface rack for use
with industry-standard size solid state I/O modules. Thesemodules provide 1500 V of isolation from harsh electricalenvironments for both digital inputs and outputs. Onboard
TTL-level drivers provide the necessary drive current tocontrol any compatible 5 V solid-state relay. The SSR senses(input) and switches (output) AC and DC voltages.

Module input/output control
OUT/IN jumpers
Two jumpers are provided to set the module type for PORT C
High and PORT C Low.


Screw terminal wiring
Each SSR-RACK08 module has two independent screwterminals. Use 12-22 AWG wire to connect signals to thescrew terminals. The status LED is ON when a module isactive.

The jumper labeled P15 controls modules 1 through 4,
which are controlled by PORT C Low bits (bit 0 throughbit 3).
The jumper labeled P16 controls modules 5 through 8,
which are controlled by PORT C High bits (bit 4 throughbit 7).

You cannot mix input and output modules within a group.

Solid-state I/O modules

The screw terminal/module numbers correspond to 8255 ports:


1 to 4 correspond to PORT C Low Bit 0 to 3
5 to 8 correspond to PORT C High bits 4 to 7

The SSR-RACK24 has eight mounting positions for solid state
I/O modules manufactured by Gordos, OPTO22, Grayhill,
Western Digital, and others. These modules provide 1500 V ofisolation from harsh electrical environments for both digital
inputs and outputs. Mounting screw threads are provided for
you to easily install the SSR modules. An example of an SSRmodule and mounting screw is shown below.

Contact MCC for compatible modules from the SSR-OAC,
SSR-ODC, SSR-IAC and SSR-IDC module series.

DS SSR-RACK08.doc
Document Revision 3, March, 2010

Copyright © Measurement Computing Corporation

SSR-RACK08 Datasheet

Page 237-pin connectors

SSR-RACK inverting logic

The SSR-RACK08 has two 37-pin D connectors labeled P14
and P20 on the board. Most pins are wired 1:1, although pins
1, 2, and 11-19 are not passed through. A typical interface
connector pin out is shown below.

On an input SSR, the presence of a voltage raises the TTL
output of the SSR from TTL low to TTL high. Because theSSR-RACK uses the conventional inverting logic, thecompleted circuit of SSR and SSR-RACK lowers the signal tothe DIO board from TTL high (+5) to TTL low (GND). An
output SSR completes a circuit when the DIO board TTL
signal to the SSR is low. The circuit through the SSR is open
when the signal from the DIO board is high.

Converting the SSR-RACK from inverting
logic
The SSR-RACK follows the convention set by OPTO22 andfollowed by virtually all SSR rack manufacturers — the senseand control logic for the relays is inverted. This means that a 0output from the digital I/O board causes an output relay toactivate (complete the circuit), while a 1 (TTL high) causes
the relay to deactivate. The chips which invert the logic aresocketed and can be easily replaced with chips that do notinvert the logic. Discuss your order with a technical sales
engineer if you need non-inverting logic.

Use C37FF-x cables to connect with compatible MCC 24-bit
digital I/O boards, such as the USB-DIO24/37. The 2ndconnector is provided to access the remaining board
connections.

Onboard buffers
Because most manufacturers of SSR racks do not supply
output buffers on the SSR rack, simple digital I/O boards suchas the PCI-DIO24, PCI-DIO96, and other manufacturer's
82C55-based digital I/O boards do not have the power toswitch the SSRs. For example, to use an OPTO22 PB16 rack,
you need to use a high-drive DIO board such as the PCIDIO24H or PCI-DIO96H.
In order to be usable with all common TTL output boards, theSSR-RACK08 is designed with onboard buffers. With thesebuffers, you can plug directly into the SSR-RACK08 fromyour PCI-DIO24, PCI-DIO96, or any other manufacturer's
82C55-based digital I/O board.

DS SSR-RACK08.doc
Document Revision 3, March, 2010

Copyright © Measurement Computing Corporation