Tri-Colour LED Diagnostic Status Indications
The Morley-IAS MI-DMMI single-channel monitor module incorporates an integrated tri-colour LED indicator visible across two distinct viewing planes (the front face and the profile light pipe). Field service engineers can view the LED directly through the transparent inspection window of the M200E-SMB (or M220E/SMB) wall mounting box without dismounting or opening the enclosure cover. Diagnostic states include:
- Pulsing Green: Confirms normal cyclic polling and successful communication between the module and the Morley-IAS intelligent fire alarm control panel.
- Steady Red: Indicates an active alarm condition triggered by the closed state of the supervised external normally open dry contact device.
- Blinking Yellow: Indicates a local loop trouble condition, input circuit fault, or activation of the integrated short-circuit isolator.
- No LED Activity (Off): Indicates absent signalling line circuit (SLC) power, incorrect line polarity, an unpolled address setting, or loop operating voltage dropping below the 17.5 Vdc threshold required to illuminate the diagnostic LED.
Loop Voltage and Standby Current Verification
When investigating communication failures, missing device reports, or intermittent polling dropouts on the Morley-IAS loop, verify electrical circuit parameters at the plug-in terminal blocks:
- Operating Voltage: Measure the DC voltage across the loop input terminals. The functional operating range is 15 to 30 Vdc. If loop voltage drops below 17.5 Vdc due to high loop resistance or excessive line loading, digital communications may continue, but reliable LED illumination will cease.
- Standby Current Draw: Without communications, the maximum quiescent draw is 310 µA at 24 Vdc. Under standard interrogation (one communication every 5 seconds with LED blink enabled), current consumption rises to a maximum of 510 µA at 24 Vdc. Higher current measurements typically indicate field wiring leakage, moisture degradation, or partial short circuits on external cabling.
Input Circuit Supervision and Contact Device Faults
The MI-DMMI provides continuous line supervision for normally open dry contact devices, including waterflow switches, sprinkler supervisory valves, pressure switches, and security contacts. The module continuously distinguishes between normal, open circuit, and active alarm states.
If the fire alarm control panel registers an open-circuit fault, check the mechanical seating of the plug-in wiring terminal block and verify cable continuity between the module terminals and the external initiating device. If the panel latches in an unexpected alarm state accompanied by a steady red LED, verify whether the external monitored contact has mechanically jammed closed or if physical wiring damage has bridged the supervisory conductors.
Addressing and Commissioning Faults
The module utilizes visible decade rotary selector switches enabling manual address selection from 01 to 99 across the Morley-IAS signalling loop. Field diagnostic procedures for addressing issues include:
- Duplicate Address Trouble: If the control panel reports an address clash or intermittent responses, visually inspect the rotary switch dials through the mounting enclosure window to confirm that the selected decade value is unique on that specific SLC loop.
- Unconfigured Address (00): Setting rotary switches to address 00 leaves the unit in an inactive state that will not be polled by the panel. Ensure the tens and units switches are positively indexed to an assigned address between 01 and 99.
- Panel Configuration Alignment: Ensure the physical rotary address matches the panel's internal device loop table and software configuration.
Integral Short-Circuit Isolator Activation
The MI-DMMI features built-in short-circuit isolators meeting EN 54-17 standards directly on the signalling line circuit. When a short circuit occurs on an adjacent segment of the SLC wiring, the internal isolator trips to isolate the damaged cable section, presenting a yellow diagnostic indicator. Service personnel should disconnect the plug-in terminal block, measure continuity and line resistance across the isolated loop conductors to clear the short, and confirm that environmental operating conditions remain within the certified range of -20 °C to +60 °C and 0% to 95% relative humidity (non-condensing).
