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Magnesonics Model MSC 900 Operation

Ultrasonic transmitters send a pulse of ultrasound down to the liquid surface and detect the reflected echo. An internal microprocessor, which is pre-programmed with the speed of sound, can then translate the time taken for the pulse to be returned into the distance between the transmitter face and the liquid surface. An integral temperature sensor in the transmitter compensates for temperature change effects on the speed of sound in the ullage space.   Having established this basic distance, the transmitter calculates the depth of liquid and sends this information back to the control unit as a 4-20mA signal proportional to level. Alternatively, a ceramic cell hydrostatic pressure transmitter can be used to sense liquid level and provide the 4-20mA signal to the control unit.

The control unit uses this information to drive control relays which can be freely assigned by the operator. Alternatively, tank contents or volumetric flow in an open channel flow application can be calculated.  There are 5 built-in relays and a 4-20mA current output A clear 4 line display on the unit shows the measured variable or may be programmed to show other operational information. A bargraph representation of the current output and relay status are also displayed.

Programming is simple and efficient using the integral membrane keypad on the face of the control unit. The menu structure is easy to navigate

The transmitter is mounted over the liquid surface using the 1 " threaded connection provided. A locking backnut and bracket is supplied which facilitates mounting the transmitter from a spar or strut above the sump. If a hydrostatic head pressure transmitter is used for level sensing, the transmitter is usually suspended in or clamped to the bottom of the sump.

The cable provided is run back to the control unit, which may be mounted up to 165 ft. away either inside or outside. Having connected the two wire transmitter cable to the appropriate terminals in the control unit and connected the power supply, the system is ready for programming with the details of the application.

Programming is simple and efficient using the membrane keypad on the face of the control unit and the "Wet well wizard " in the menu.

Pump control relays and functionality The MSC pump control system has 5 relays which may be allocated to control or alarm duty, all programmed independently and all freely assignable To meet the needs of the water industry, the following features are provided as standard: -

• All relays have an adjustable band with user defined on/off points
• Up to 4 pumps can be controlled using 4 of the relays, either in standard sequential mode or in one of the popular control routines: Duty / Standby Duty / Assist
• Pumps can have common or independent off levels
• Choice of manual select or autosequence for the lead pump
• Scum line prevention routine to vary trip points and avoid scum build up
• Real time clock allows override of control routine to empty sump during low cost electricity periods P
• Time delay between relay-on signals prevents electrical or hydraulic overload
• User defined periodic pump down routine and frequency to empty sump
• Relay energised or "run times" are logged and stored to enable monitoring of pump run times.
• Calculation of pumped volume allows pump efficiency to be monitored and reported should efficiency fall below a user defined value.

5th relay is normally a failsafe alarm relay (loss of echo, mains failure or other system fault) but may be re­programmed as a standard alarm or control relay. Any relay can be programmed as a rate of rise or rate of fall alarm, temperature, level, contents or flow out of limits alarm or pump efficiency alarm.