Emerson IP221 User Manual
Instructions Leaflet
IP221, Rev. AA
November 2004
Mobrey
Level
Electropulse systems
Safety Information 2
1. Introduction
1.1 Sensors 3
1.2 Interface detection 4
1.3 Sludge density detection 5
1.4 Head amplifier units 5
1.5 Control Units 6
2. Installation
2.1 Calibration 7
2.2 Sensor and head amplifier installation 10
2.3 Control Unit Installation 12
2.4 Wiring 12
2.5 Intrinsically safe application 15
3. Fault Finding 16
4. Specification and description
4.1 Sensors 17
4.2 Head amplifiers 17
4.3 Control Units 18
5. Recommended Spare Parts
For instructions specific to units
used in hazardous area
installations
refer to leaflet IP221/SI
Appendices
Appendix I Part Numbers 20
Appendix II List of illustrations 22
Appendix III List of tables 22
Maintenance / Inspection 23
Contents
Gap Sensors
Hi-Sens
Attenuation method
Reflection method
Normallay acting
Inverse acting
Summary
Cables
Head amplifier
Control Unit
www.mobrey.com
1
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.
A supply disconnection device must be included in the installation, fitted as close as practical to and
not be obstructed by the equipment. It must be double pole and marked as the disconnection device.
Each relay circuit must be protected by a fuse not exceeding the maximum rated current for the relay
as specified in the manual.
On wall mount unit disconnect supply before removing control unit from base. Control units must be
correctly assembled to achive stated IP ratings.
Explanation of symbols :
The IEC symbols used on the equipment are as follows :
Refer to Manual.
!
The Protective earth terminal must be connrected to an external Protective earthing system.
Functional earth terminal. |f this terminal is used it must be connected to an external
earthing system at the same potential as the protecive earthing system.
2
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. When immersed in a
liquid the signal transmitted is carried by the liquid across the gap, to the receiver, when the liquid level
drops below the sensor, the signal cannot be carried across the gap, and is not received by the second
transducer.
b) Hi-Sens cylindrical sensors
The Hi-Sens sensor consists of two ultrasonic transducers mounted
on the inside of a cylinder. When the sensor is not submersed in
the liquid the signal from one transducer resonates round the
cylinder like a bell ringing. If the liquid rises up around the
sensor, this ringing is damped and the signal received by the
second transducer is significantly reduced. This reduction is
monitored by the head amplifier unit. Switching occurs when the
liquid is about half way up the cylinder.
Figure 1.2 - Hi-Sens, cutaway to show
construction
Use of Hi-Sens transducers in high alarm applications, and gap
sensors in low level alarm applications achieves a Failsafe system
in which any sensor or cable failure will be indicated as a fault or
an alarm by the control unit.
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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. In this case the
gain of the control unit is set so that the relay is energised only when the liquid with the lower
attenuation is in the gap. For this application Sensor Type 402S is used horizontally. The heavy-duty
sensor type 433S may also be used, perhaps from above on an extension tube. For use in pipes, the
sensor pair 442S should be mounted in line, facing one another, generally horizontally across the
diameter, to detect the interface or presence of liquid. As an example, the interface between oil and
water can be detected using this method.
OIL
Receiver Crystal
Sensor in Oil. The ultrasonic beam is
attenuated and will not reach the
receiver crystal.
WATER
Receiver Crystal
Sensor in Water. The ultrasonic beam
reaches the receiver crystal.
Transmitter Crystal
Figure 1.3 - Attenuation Method
Transmitter Crystal
Reflection Method – Figure 1.4
If the attenuation’s are similar and the attenuation method does not work, then the reflection method
must be used.
If an ultrasonic beam is transmitted from one liquid to another at a suitable angle, it does not go
straight through the interface, but is bent, so that it does not reach the receiver crystal. If there is no
interface in the gap, but only one liquid, then the beam travels in a straight line, is received and the
relay energised.
For this application the sensor must be mounted at about 10º from the horizontal, as shown in Figure
1.4. Note that this method gives an alarm only when the reflective surface of the interface itself is at
the sensor.
Oil
Water
Sensor in lower liquid. The ultrasonic
beam reaches the receiver crystal.
Figure 1.4
Oil
Receiver
Crystal
Water
Transmitter
Crystal
Sensor at interface level. The ultrasonic
beam is reflected/refracted and will not
reach the receiver crystal.
In order to differentiate between two liquids, interface sensors have a large gap (usually 150mm) and
oscillate at 3.75MHz.
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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 1.5 shows the operation of the sensor. In a clear liquid the ultrasonic signal is carried across
the gap so the sensor oscillates and the control unit gives a ‘Normal’ indication. When a sludge is
present this scatters the signal as shown in Figure 1.5(b) The signal is attenuated, and the control
unit gives an alarm indication.
1.4 Head Amplifier Units
The head amplifier is mounted on the end of, or near to the sensor. It converts the low level high
frequency signal of the sensor into a series of low frequency current pulses that are sent to the control
unit. These pulses are virtually immune to electrical interference.
This means that the length of the cable between the head amplifier and the control room can be 1km
or more. There are five versions available, which fall into two categories:
i) Normal acting head amplifiers
When the sensor is in its normal state (i.e. Dry for Hi-Sens and Wet for Gap Sensors) the signal from the
transmitting transducer is received by the second transducer, and fed back to the head amplifier
causing it to transmit current pulses to the control unit. If an alarm state occurs the sensor no longer
oscillates, and the head amplifier stops transmitting the pulses. The control unit indicates the alarm
condition.
Thus in the normal state, the whole system is active. If a fault occurs in the electronics then the
pulses cease and an alarm state is indicated immediately. In this way the whole circuit is continually
monitored. This is in addition to the fault checking facilities of the control unit.
There are four versions of the normally acting head amplifier. Usually it is possible to mount the head
amplifier on the sensor, but it may be necessary for reasons of temperature or space, to use a head
amplifier which is mounted adjacent to the sensor, and is connected to it by a short length of coaxial
cable. Both of these types are available either in an industrial case, or a heavy-duty case that is
suitable for open deck mounting in marine applications.
The sensor mounted marine head amplifier may contain a double circuit board for use with dual HiSens or gap sensors.
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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.
• High temperature, corrosive, or aerated liquids, where Gap Sensor can be used at high level if
required.
The head amplifier transmits pulses when the sensor is not oscillating (its normal state), and stops
transmitting in the alarm condition when the sensor is oscillating. Thus the normal light on the control
unit indicates a wet Hi-Sens, or dry gap sensors. When the inverting amplifier is used the sensor is in
its quiescent state for most of the time. For this reason sensor cables can be monitored to check for
cable breaks with some sensors.
Note that when an inverse acting head amplifier is used the sensor is not oscillating under normal
conditions and therefore the integrity is not as high as that of a normally acting head amplifier, which
should be used wherever possible.
Inverse acting amplifiers are only available in adjacent mounting industrial housings.
Summary of sensor head amplifiers
1.1
1.2
Type
Sensor mounting
Adjacent mounting
Inverse acting
Sensor State
Hi-Sens Dry
Lo-Sens Wet
Hi-Sens Wet
Lo-Sens Dry
Industrial Case
***S*PI***
MEP*AI
MEP*XI
Normally acting head
amplifier *PI*, *PM*, AI
Normal State
Pulses transmitted
Green light on c.u.
Alarm State
No Pulses transmitted
Red light on c.u.
Marine
***S*PM***
-
Output
Inverse acting head
amplifier XI
Alarm State
No Pulse transmitted
Red light on c.u.
Normal state
Pulses transmitted
Green light on c.u.
Sensor cable check circuitry is built into the industrial adjacent mounted head amplifiers, where the
coaxial cable linking head amplifier and sensor may be exposed on site. This is only operable where
the sensor in use has Earth continuity between the two coaxial cables, see section 2.2 Lack of screen
continuity along these cables causes the head amplifier to signal a fault condition to the control room
readout unit. To use the facility a wire link in the head amplifier must be cut during installation.
(See section 2.2)
1.5 Control Units
The control unit is available in two forms, a free standing plastic case (MEP*L), or a rack mounting
unit (MEP*R). Operation is the same in either case.
Front panel indicators show normal condition (green), alarm (red), and fault (amber). A front panel
switch to test fault and alarm circuits is provided, together with a variable time delay for the alarm
circuit.
Relay contacts are provided to indicate an alarm condition. A second relay is supplied on rack
mounting control units to indicate a fault. On both units, a fault also causes an alarm to be
indicated.
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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. The head
amplifier unit should be wired to the control unit, which should be connected to its power supply.
Wiring instructions are given in section 2.4.
When the mains supply to the control unit is switched on, either the green ‘normal’ light or the red
‘alarm’ light should be on, the amber ‘fault’ light should be off. The lid of the head amplifier unit is
removed by undoing the four screws or Allen bolts. Care should be taken not to damage the sealing
gasket, which should be replaced with the lid. When using integral head amplifiers, the sensor must
not be unscrewed from the head amplifier unit as this is likely to damage the internal wiring (and may
violate ATEX approval).
i) ***S*PI
ii) ***S*PM
Figure 2.1 - Head
amplifier internals
iii) MEP*AI and MEP*XI
The marine head amplifier ***S*PM has one gain potentiometer for each sensor attached. It is factory
calibrated for the side range of liquids carried on tankers. It is advisable to check the function of the
system before final installation, using a sample of the liquid. The gain potentiometers are covered by
a screw cap, which should be replaced after re-calibration.
The industrial head amplifiers ***S*PI, MEP*AI and MEP*XI have a gain switch, which is illustrated in
Figure 2.2 (i) and 2.2 (iii).
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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).
4) Gradually increase the gain until the control unit indicates ‘normal’ (or ‘alarm’ for inverse acting
control units). This is beginning of the operating band.
5) The optimum gain setting can be found by rotating the potentiometer a further 30º (one division on
the clock face),
6) Check that the control unit switches satisfactorily when the sensor is immersed in the liquid.
ii) Gap Sensors
1) Ensure that the sensor is clean, and immerse it in a sample of the liquid, making sure that the gap
is full of the liquid, and unobstructed. Adjust the time delay on the control unit fully anticlockwise.
2) Set the head amplifier gain control fully anti-clockwise, with the gain switch (if fitted) in the high
gain position.
3) The control unit should now indicate alarm (or normal for inverse acting head amplifiers) if it does
not switch to low gain (if a gain switch is fitted).
4) Gradually increase the gain until the control unit indicates normal (or alarm for inverse acting
head amplifiers). Note the position of the potentiometer and gain switch. This is the lower end of
the working range.
5) Remove the sensor from the liquid, and allow the liquid to drain away. Ensure that nothing is
touching the sensor body. The control unit should now indicate alarm (or normal for inverse
acting head amplifiers).
6) Gradually increase the gain until the control unit indicates normal (or alarm for inverse acting
head amplifiers). Note the position of the potentiometer and gain switch. This is the upper limit
of the working range.
7) The optimum gain setting is midway between the points recorded in steps 4 and 6. It may be
necessary to estimate this point if the gain switch has been used.
8) Check that the control unit switches correctly when the sensor is immersed in the liquid.
iii) Interface Sensors – Attenuation Method
1) Ensure that the sensor is clean, and that the delay on the control unit is fully anti-clockwise.
2) With the sensor in the lower liquid adjust the gain potentiometer anti-clockwise, using the gain
switch if necessary, until the control unit changes from ‘Normal’ to ‘Alarm’.
3) Note the position of the potentiometer. If the control unit does not switch to ‘Alarm’ use the
bottom end of the scale as a reference.
4) Immerse the sensor in the upper liquid. The control unit should now indicate ‘Alarm’. If it does
not then the reflection method should be used.
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