Instructions Leaflet IP221, Rev. AA November 2004 Level Mobrey Electropulse systems Contents Safety Information 1. Introduction 1.1 Sensors Gap Sensors Hi-Sens 2 1.2 Interface detection Attenuation method Reflection method 4 1.3 Sludge density detection 5 1.4 Head amplifier units Normallay acting Inverse acting Summary 5 1.5 Control Units 6 2. Installation 2.1 Calibration 2.2 Sensor and head amplifier installation 2.3 Control Unit Installation 2.4 Wiring Cables Head amplifier Control Unit 2.
Warning : If this equipment is used in a manner not specified by the manufacturer, the protection provided may be impaired. All installation and commissioning of this equipment must be carried out by electrically competent persons. Protection of permanently installed equipment : This equipment is regarded as permanently installed equipment. Ensure wiring is suitable for the load current and the insulation is suitable for the voltage, temperature and environment of the installation.
1. Introduction The Mobrey Electropulse system is used for the detection of liquids or liquids with suspended / settled solids. It consists of three units, a sensor, a head amplifier unit, and a control room unit. 1.1 Sensors There are many different Mobrey sensors available, but they fall into two categories: a) Gap sensors Figure 1.1 - Gap sensor, cut away to show construction Gap sensors feature two ultrasonic transducers mounted one either side of the gap.
1.2 Interface detection Attenuation method – Figure 1.3 Attenuation is the reduction in strength of the ultrasonic signal caused by its transmission through a liquid. Viscous liquids, emulsions and liquids containing solid particles have a greater attenuation than clear thin liquids. Usually the difference in attenuation between the two liquids is sufficient and the attenuation method can be used to determine which liquid is in the sensor gap.
1.3 Solids Density Detection The Electropulse system can be used in conjunction with a 433S type sensor to provide blanket level detection in settling tanks, facilitating the control of automatic de-sludging. In addition the Electropulse system can be used to detect the solids density of a slurry in a pipe line. In this case the Mobrey pipe section is used instead of the sensor. Figure 1.5 - Sludge density sensor, operation (a) Clear liquid, signal transmitted (b) Solids attenuate the signal Figure 1.
ii) Inverse acting head amplifiers When it is required to use a Hi-Sens sensor for low level detection, or a Gap Sensor for high level detection, an inverse acting amplifier must be used. Examples of this are given below: • Hi-Sens can be used to detect low levels in very light liquids or foams. • A miniature Gap Sensor 366S, may be used to detect high level when there is insufficient room for a Hi-Sens.
2. Installation 2.1 Calibration When installing the sensor, it should be remembered that it is measuring instrument, and should be treated with care. Before installation the sensor and control unit should be inspected for transit damage, the gap faces of gap sensors must be parallel. Before installation, the equipment should be calibrated, if possible, using a representative sample of the liquid in which it is to be used.
Calibration procedure by sensor type i) Hi-Sens Sensors 1) Ensure that the sensor is clean and dry, that nothing is touching the sensor body, and that the delay adjustment on the control unit is fully anti-clockwise. 2) Set the gain potentiometer in the head amplifier fully anti-clockwise, and the gain switch (if fitted) in the low gain position. 3) The control unit should now indicate ‘alarm’ (or ‘normal’ for inverse acting head amplifiers).
5) With the sensor in the upper liquid, increase the gain, using the switch if necessary, until the control unit changes to ‘Normal’. Note the position of the potentiometer. If the control unit does not change to normal then the end of the scale should be used as a reference. 6) The gain should be set half way between the settings found in steps 3 and 5. 7) Check that the unit switches correctly giving a normal indication in the lower liquid and an alarm indication in the upper liquid.
2.2 Sensor and head amplifier installation Make sure that there is room inside the tank for the sensor without anything touching it, and that the gap is not obstructed. At least an inch of clearance must be left around Hi-Sens senors. The head amplifier should have its cable glands downwards if possible to reduce the possible to reduce the possibility of ingress of rainwater. For threaded sensors a hole is drilled in the tank at the appropriate level, and this is tapped to take the sensor.
* DIN RAIL Mounting Clip available on request Figure 2.
2.3 Control unit installation The control units should be installed in an area suitable to their specifications. They are designed to be used indoors, but could be installed outside using a suitable weatherproof enclosure. The front panel should be accessible to the operator. The standard control unit MEP*L is installed by undoing the two screws on the top and bottom of the unit, and removing the base.
ii) Head Amplifier Unit The head amplifier terminals A+ and B- should be connected to the cores of the control unit cable. In the case of the dual marine unit, lower sensor connections A+ and B- are connected to the two cores of one cable, and upper sensor connections, C- and D+ to the other. The screen should not be connected in any head amplifier unit, as this could cause an earth loop. The marine head amplifier has cable grips which should be used.
MEP 3B I.S. To head amplifier Screen to be connected Relays Protective Earth Neutral Live MEP 3L I.S. Figure 2.
2.5 Intrinsically safe installation Control units type MEP3* and head amplifier units to type MEP3** and ***S*P*H** are approved by ATEX as intrinsically safe equipment to II 1 G Ex ia IIC. Refer to safety instruction IP221/SI and local code of practice. The following points must be noted when installing these units:i) The cable from the head amplifier to the control unit must be screened, and the screen must be connected at the control unit end only. ii) On I.
3. Fault Finding If the unit does not work as described in the text, this section suggests some simple checks which will rectify most faults. If the system still ceases to work or there is any doubt as to its working, the factory should be consulted. IT SHOULD BE NOTED THAT SOME OF THE TESTS BELOW VIOLATE I.S. REQUIREMENTS AND SHOULD NOT BE ATTEMPTED ON I.S INSTALLATIONS. If in doubt please contact the factory. The first test is always to check the mains supply voltage.
4. Specification and Description 4.1 Sensors Sensor Type Minimum Temperature ºC Maximum Temperature ºC Maximum Pressure Kg/cm2 Fitting Frequency 302S 30HS 312S 312SP 323S 352S 362S 366S 373S 393S 39HS 402S 420S 433S 442S HL*S -70 0 -70 -70 -70 -70 -210 -210 -70 -70 0 -70 -70 -70 -70 -70 150 250 130 130 130 150 65 65 150 150 250 150 150 150 150 130 56 50 21 20 21 56 70 3.5 56 56 50 103 280 105 105 100 R¾” R1½” R1” R1” R¾” R¾” R¾” M6 R¾” R¾” R¾” R¾” ¾” NPT R¾” R¾” Flange or screw 1 1 1 1 1 1 3.
4.3 Control Units Supply: Rack Mounted Unit MEP*R Free Standing Unit MEP*L 1: 220/240V ±10%, 50/60Hz 2: 110/120V ±10%, 50/60Hz Power consumption: Less than 7VA Output: Alarm relay DPCO relay, energised in normal mode, releases on fault or alarm Connections: Terminal block on the rear of the Screw terminal in the base of the rack unit. case. To take wires up to 1.5mm2 See Figure 2.7 for wiring details Earthing: Mains input and sensor connections are fully floating with respect to earth.
5. Recommended Spare Parts 5.1 Sensor and head amplifier Sensors and head amplifiers are supplied as integral items, and therefore no spare parts are available. In the case of sensor mounted head amplifiers, the sensor is attached to the head amplifier, and the two are not usually available separately. 5.
Appendix I - Part Numbers Please note that the existence of a part number does not imply the availability of a unit. 1.
3. Control Units MEP3L/1D Intrinsic Safety Mounting Mains Voltage Output Relay 3 R L 1 220/240 Volts 2 110/120 Volts S D Intrinsically Safe Rack Mounted Wall Mounted Single Pole Changeover Double Pole Changeover 4.
Appendix II – List of illustrations Section Figure Title Page 1. Introduction 1.1 1.2 1.3 1.4 1.5 Gap Sensor Hi-Sens Sensor Attenuation Method Interface Method Sludge Density Sensor 3 3 4 4 5 2. Installation 2.1 2.2 2.3 2.4 2.5 2.6 Head Amplifier Adjacent head amplifier Control unit mounting details Wiring Summary Sensor connections to adjacent head amplifier Control unit connections 7 8 11 12 13 14 Appendix III - List of tables Section Table Title Page 1. Introduction 1.1 1.
Maintenance / Inspection This is limited to periodic inspection by a qualified person to ensure that the installation including wiring and equipment housing is safe. Clean only with a damp cloth, ensuring that no moisture enters control unit. Check unit for damage and if damaged do not use.
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