The Bently Nevada 3500/77M Cylinder Pressure Monitor is a 4-channel monitoring module designed as part of the 3500 Series machinery protection system for reciprocating compressors. It accepts inputs from Bently Nevada approved pressure transducers and conditions these signals to provide critical pressure measurements, continuously comparing them against user-programmable alarm setpoints for machinery protection .

Each of the four channels provides up to eight measured variables related to cylinder pressure operation. For each cylinder chamber, key calculated values include Discharge Pressure, Suction Pressure, Maximum Pressure, Minimum Pressure, and Compression Ratio. The monitor also provides Peak Rod Compression, Peak Rod Tension, and Degree of Rod Reversal to assess dynamic loading on compressor rods .

The module offers high accuracy, with pressure readings accurate to within 0.5% from 0.5 to 10.0 volts at 77°F (25°C), and 1.0% over the full operating temperature range of -30 to 65°C (-22 to 150°F). It includes a built-in transducer power supply providing 23.0 ±0.8 Vdc with current limiting. Front panel LEDs provide clear indication of module OK status, communication activity (TX/RX), and Bypass mode, enabling operators to quickly assess the health and operational state of the monitor .