On the display
The display reads SPS CPU Fault. The manuals print the message only in this one form, so this is the exact text shown on the control unit.
What it means
SPS CPU Fault is a hardware fault signal of the 4100ES, not a programmed software point. The Fault (Trouble) relay on the Alarm Relay Card is link connected to this hardware signal. When the SPS loses communications with the CPU, that relay signals “Fault”, and the panel shows this message.
The manual draws one practical conclusion from this wiring: an Aux relay programmed as normally energised (de-energising on Fault) cannot be used to replace the Fault relay on the Alarm Relay Card. Only the Fault relay itself is link connected to the “SPS CPU Fault” signal, so a substituted Aux relay will not follow this hardware signal. This is why the manuals take the message up in their brigade interface material, where the Alarm Relay Card and its Fault relay are used.
Why it appears
- The SPS loses communications with the CPU; the Fault (Trouble) relay on the Alarm Relay Card, being link connected to the “SPS CPU Fault” hardware signal, then signals “Fault”.
Questions engineers ask
What does “SPS CPU Fault” mean on a Simplex 4100ES?
It is a hardware fault signal that operates when the SPS loses communications with the CPU. The Fault (Trouble) relay on the Alarm Relay Card is link connected to this signal and signals “Fault”.
Why does my 4100ES show SPS CPU Fault?
The manual gives one cause: the SPS has lost communications with the CPU. When that happens, the link-connected Fault (Trouble) relay on the Alarm Relay Card signals “Fault”.
Can a programmed Aux relay replace the Fault relay on the 4100ES Alarm Relay Card?
No. The manual states that an Aux relay programmed as normally energised (de-energising on Fault) cannot replace the Fault relay, because the Fault relay is link connected to the “SPS CPU Fault” hardware signal.
Messages next to this one
Source
Written from the manufacturer's manuals for the Simplex 4100ES; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All Simplex 4100ES messages: fault codes · Simplex 4100ES documentation · Simplex manuals