Topology

The Fault Insertion Unit (FIU) section of the OP8900 boards consists of seven relays per differential pair of signals, for a total of 112 relays (7 x16).

Each relay can be controlled individually.

For each group of 7 relays, the possible faults are

Open-circuit of the pair
Short-circuit of the two signals of the pair
Two fault injection, with two user-supplied voltage references voltages (VBusA and VBusB), for each signal of the pair.

Note: Diagram only shows one channel.

Embedded Protections

The following protections are implemented:

In the default state, all relays are open
All channels are updated simultaneously
VBusA and VBusB cannot be connected on the same channel at the same time: VBusA and VBusB cannot be shorted
When the Signal + and Signal - are shorted together, only one other fault is allowed for VBusA or VBusB on that channel pair
Relays on a channel are always open before closing any other

The maximum peak current per relay is 1A. There is no over-current protection

The relay technology used in the FIU allows a higher density and has a fast response time (<0.5ms). However, this technology is very sensitive to peak current, even for a few micro-seconds. It is the customer's responsibility to limit the peak current by adding the resistor on the signal or VBus based on the capacitor and cabling present on the circuit.

Even if the power supply on the VBus is limited to 0.1A, a capacitor is present at the output and the peak current can easily >5A before the internal current limit kick in creating permanent damage to the relay.

If a relay is broken in short mode, an RMA can be issued to repair the card. If the customer has access to a technician with valid IPC-610 certification and experience with a rework of through-hole lead-free and no-clean soldering, OPAL-RT authorizes this technician to replace once a faulty relay.

Here is a short recap of the process:

Remove the SLSC card out of the SLSC chassis.
With a basic multimeter measure the impedance between pin 1 and 4 of all 112 relays. If <100R, the relay needs to be changed.
Unsolder the faulty relay. No-clean flux can be used.
Solder a new relay: Comus International 3570-1419-054.

For output signal (analog or digital), always open the load relay (relay in series of the signal) when creating faults to prevent damage on the output circuit.

Even if some protection is built-in on the output circuit to prevent damage, creating a direct fault to VBus with higher voltage can create permanent damage.