For 28 years, the Medway Tunnel, underneath the River Medway, which connects the towns of Chatham and Strood in Kent, England, has relied on accurate water level monitoring to guarantee a safe passage for over 40,000 vehicles per day.
The tunnel has four strategically placed sumps, one at each end and two in the centre, and these sumps collect any water from the River Medway and road runoff. Shortly after the tunnel’s opening in 1996, our PSM level transmitters were installed in each sump.
The 4-20mA signals from these transmitters are fed into a PLC system that controls the pumping out of sumps, when the level reaches a predefined point, crucial for optimal water management, Because the level is controlled within a defined range, the transmitters were required to provide accurate measurement over a small range – 450mm for the central sumps and 1300mm for the larger end sumps, providing precise data within this critical zone.
The PSM transmitters have delivered exceptional performance throughout the tunnel’s operation. One transmitter is the original unit installed in 1996, while two were replaced in 2006 and two upgraded in 2009, meaning even the newest has worked reliably for over 15 years.
Recognising the critical role these instruments play, PSM is contracted to conduct annual checks and calibration certifications. These checks are performed during nighttime closures of the tunnel to ensure safety, and these inspections often reveal that the transmitters have maintained their accuracy, requiring no or minimal adjustments year after year.
