Feature: System Security
Following installation, the liſts began experiencing issues.
Te fire control input became active when the liſt was in travel, despite the contact driving the input remaining open. Te liſt would randomly descend to the ground floor and be out of service, so passengers couldn’t call it from their floor. Aſter extensive
investigations, we established that the issue was external and unrelated to the control system,” John Merrill said. “As a temporary
solution, we installed a galvanically-isolated contact that interfaced into the controller as a countermeasure to break the connection to the fire control input. While this was effective, we needed a more permanent
Keeping
residential lifts running
By John Merrill, Managing Director, Schneider Lift Controls, and Nick Price, Team Leader – Elevator, CP Automation
H
aving established the liſt system wasn’t at fault, CP Automation supplied the liſt manufacturer Schneider Liſt Controls with the devices, which almost immediately reduced voltage distortion and stopped the fire control input from randomly becoming active and halting the cab’s travel.
Like many residential buildings, the premium-serviced
apartment complex uses liſts to transport residents and ensure accessibility, and the system had been installed by Schneider Liſt Controls, an approved UK and Ireland supplier for the LiSA control system.
22 June 2025
www.electronicsworld.co.uk
solution. At this point, we brought in CP Automation.” CP Automation conducted a power quality survey and initial
frequency measurements revealed a cycle time of 125µs, matching the 8kHz carrier frequency of the variable speed drive (VSD). Further analysis detected harmonic disturbances up to
104kHz, with poor-quality earthing emerging as an issue. Supraharmonic levels exceeded acceptable limits, and during our visit the site’s total harmonic distortion voltage (THDv) was close to the acceptable limit. Te THDv will vary according to the local loads on the supply
outside of the control of the site, so there’s a risk this limit could be exceeded at other times of the day. Aſter assessing the panel wiring and earthing, no faults were found in the liſt’s setup, confirming that external power quality issues were to blame. Nick Price said: “Once we’d confirmed the issue was external, we
focused on mitigating the distortion at the points we could access. “We installed a SineTamer sine filter and surge protection
device (SPD) at the three-phase input terminals inside the control panel. Tis allowed us to tackle the problem directly at the source, reducing the impact of electrical noise on the liſt system.” “A SineTamer isn’t just a standard SPD. It uses frequency
attenuation circuitry, meaning it actively tracks and follows the sinewave form, protecting all 360 degrees of it. “Aſter installing the SineTamer, we immediately saw a reduction in the peak voltage distortion,” added Price. “It dropped from 11V at 40kHz, 56kHz and 73kHz to 2.5V at 88kHz, a reduction of around 80 per cent.”
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