The Model 661 Alarm Control, part of the 600 series line of instrumentation controls, is designed to monitor and maintain measurable applications such as liquid levels, temperature, pressure, flow, etc. A user-provided 4-20mA current loop represents the measurable application, and output connections are provided for signal alarms. Two setpoints, the HIGH ADJUST, and the LOW ADJUST, are field adjustable. If the input is between the two setpoints, the relays are energized. If the input is above the high setpoint, the HIGH ALARM relay de-energizes to provide a tripped condition. This tripped condition will automatically reset when the input falls back below the setpoint. If the input falls below the low setpoint the LOW ALARM relay de-energizes. The tripped condition resets when the input rises back above the setpoint.

The Model 661 is equipped with top-mounted LEDs for trip status indication. A HIGH ALARM or LOW ALARM LED turns OFF in a tripped condition. The INPUT LOOP ERROR LED turns ON if the input is outside the 4-20mA range. A Time Mark Model 650 Loop Power Supply (or equivalent) is required to provide DC operating voltage. A Time Mark Model 672-15 Pressure Transducer (or equivalent) is required to provide the input signal.