Emerson MCU200 User Manual
Installation Leaflet
IP227, Rev. AA
July 07
MCU200 Installation, Operation &
Maintenance Instructions
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
Mobrey ultrasonic liquid level control or sludge
blanket or interface detection systems using
control unit type MCU200
MCU200
Contents
1. Sensor installation
2. Control unit installation
3. Applications:
3.1Gain adjustment
3.2Liquid level alarm
3.3Pump control and latching arms
3.4Blanket or interface detection
4. Spare parts and fault finding
Each Mobrey ultrasonic control system requires a sensor to
suit the specific application, plus a control unit.
These installation instructions cover the Mobrey control units
in the MCU200 series.
Specification
Power supply MCU 201 110/120 ±10% 220/240±10% 50-60 Hz
Installation category MCU 201 II-IEC664 for 230V ac supply III-IEC664 for 115V ac supply
Pollution degree MCU 201 2-IEC664
Power consumption MCU 201 6VA approx at 240 Vac
Power supply MCU 203 24V dc (20V Min, 30V Max) Supply must be floating or negative earth
Current consumption MCU 203 0.1A Max
Relay output 5A at 230V ac DPCO
Relay state Normal state selectable energised/de-energised
Relay delay 0.5,2,8,30 seconds selectable. Operates for change of relay state in
one direction only. 50msecs in other direction. (Approx.)
LED indicators Red for alarm, Green for normal, Yellow for cable fault
LED state Green/Red indication selectable for either sensor state
Sensors compatible Any Mobrey ultrasonic gap, Hisens or Interface sensor
Sensor frequency Switch selects electronics operational at either l MHz or 3.7 MHz
Cable check Option selectable for certain sensors
External input Used to hold relay de-energised to provide pump control
Box size 200 x 120 x 75mm
Fixing centres 188 x 188
Box rating IP65 Polycarbonate (clear lid)
Temperature -40
Holes for glands 3 off 16mmØ
EMC Emissions: EN50081-1 Immunity: EN50082-1
Safety EN61010-1
o
C to 55oC ambient
www.mobrey.com
1. Sensor Installation
1.1 General description
Each Mobrey ultrasonic sensor contains two piezoelectric
crystals. A high frequency signal (1 MHz or 3.7 MHz)
generated by the control unit is transmitted to one
piezoelectric crystal by coaxial cable. This crystal converts the
electrical signal into an ultrasonic oscillation.
The sensor design allows the ultrasonic oscillation to pass from
the transmitter crystal to the receiver piezoelectric crystal.
Most Mobrey sensors (300 or 400 series) are “gap” type
sensors, where the two piezoelectric crystals are separated by a
gap. When the gap is in liquid the signal reaches the receiver,
because of the low ultrasonic attenuation of the liquid. When
the gap is filled with air, no ultrasonic signal can pass from
transmitter to receiver.
See figure 1.
Fig.2. Hi-Sens transducer
The Hi-Sens sensor consists of two ultrasonic transducers
mounted on the inside of a cylinder. When the sensor is not
submerged 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
attenuated. The ringing or oscillation of the sensor is
detected by the control unit. Switching occurs when the
liquid is about half way up the cylinder of the Hi-Sens body.
NOTE: For satisfactory operations the Hi-Sens must not be
positioned in a vessel or tube less than 100mm internal
diameter.
Fig 1.
When the gap is filled with liquid, the piezoelectric receiver
crystal converts the ultrasonic wave into an electrical signal,
which is transmitted back to the control unit using a second
coaxial cable. Usually the two coaxial cables to the sensor are
in one overall sheath. The control unit circuitry is a feedback
amplifier, which oscillates when the sensor is wet, and is
quiescent for the sensor dry. The “oscillating” or “nonoscillating” sensor states dictate the output relay states of the
MCU200.
For sludge blanket or interface detection the sensor
“oscillates” in a clear liquid, and is “non-oscillating” in the
sludge or at the interface. The amplifier gain adjustment
determines the sludge density for the change between these
two states. See section 3.4.
For Mobrey Hisens sensors, (type numbers HL, HD etc) the
metal body of the sensor provides the ultrasonic coupling
between the piezoelectric crystals. This coupling is reduced
when the sensor is under a liquid, so that for Hisens sensors
“oscillating” state is dry, in air, and the “non oscillating” state
is wet, submerged in a liquid.
1.2 Switching levels and orientation
Mobrey gap sensors should normally be mounted with the gap
vertical, to avoid build up of solids on the sensor faces on
either side of the gap. In this condition the switching level
will be half way up the face: if the sensor is mounted from
the side of the tank this is normally on the centreline of the
cylindrical body.
Occasionally such sensors are mounted with the sensor faces
horizontal, either to avoid air bubbles passing through the gap
or for convenience of installation.
In this case the switching level will be at the sensor face at
the top of the gap.
1.3 Installation of sensor
The sensor must be handled with care - it is a measuring
instrument. Before installation, check that sensor, cable and
control unit have not been damaged in transit. Drill and tap a
hole with a suitable thread. It is advisable to use a boss or
similar on thin walls. The sensor has a tapered thread. Use
PTFE tape or similar to seal the thread. Mark the sensor
hexagon to identify the gap orientation of the sensor, if
appropriate. Take care not to damage the sensor cable during
tightening.
The cable should be laid on cable trays and separated from
any high voltage or mains cables. The normal cable
termination is a plastic gland (to fit the MCU200 control box
drilled hole) and crimped terminal pins to suit the MCU200
terminals.
1.4 Extension cables
Extension Cables up to 50 metres long can be fitted to most
Mobrey ultrasonic sensors in the factory to special order but a
better site arrangement is to have a separate extension cable.
When double coaxial cable needs to be extended, two sets of
coaxial plugs and sockets will be needed, one set for transmit
and one receive.Care must be taken that the connectors are
not earthed or shorted together in any way, to prevent crosstalk or pick-up. The coaxial connections must be made in a
waterproof junction box. Terminal blocks should not be used.
The extension cable needs to be of 50ohm characteristic
impedance. Suitable dual coaxial extension cables can be
purchased from KDG Mobrey (Part No. K178).
For extensions over 50 metres it is recommended two runs of
single coaxial low loss cable is used, with the transmit and
return cable runs separated by 0.15 metres to minimise crosstalk.
If several sensor cables are being run together then all the
transmit cables (those connected to E2) should be grouped
together and all receive cables (those connected to 1E)
grouped together maintaining the separation specified above.
2. Control Unit Installation
2.1 Mechanical
The control unit is supplied with three holes drilled in the
bottom (longer) side of the box. Two glands are supplied for
the power input cable and relay output cable. The sensor is
normally supplied fitted with a suitable gland on the cable.
Two further holes can be drilled in the bottom side of the box
should these be needed: it is recommended that the circuit
board is removed whilst drilling extra gland holes.
Fig. 4 MCU200 housing dimensions
All cable connections are made to the terminal blocks along
the bottom edge of the pcb (see fig.5). Release the terminal
screw before inserting the wire.
2.2 External Connections
Protection for permanently installed equipment
NOTE: This equipment is regarded as permanently installed
equipment and must be wired up using suitable cable for the
current and voltage specified. A suitable switch or circuit
breaker must be included in the installation and this should be
in close proximity to the equipment and marked as its
disconnecting device. A suitable fuse rated at 3A must be fitted
in the supply. Each relay circuit must be protected by a fuse not
exceeding the maximum rated current for the relay as specified
in the manual.
Fig 3 Suitable extension cables
50mtr 50-100m over 100m
RG174 URM76 Consult
RG178 RG58 factory
Two cables are required per sensor. The RG178 should be
used where the cable itself is subject to temperatures
exceeding 74°C.
(i) AC Mains is connected between the “N” terminal for
neutral and one of the “115V” or “230V” terminals
depending on the voltage supply available - BEWARE - the
terminal not connected externally will be “live” once the
transformer is powered via the other terminals.
(ii) Protective earth
NOTE: A protective earth should be used for all applications
(iii) The DPCO relay has two sets of contacts. These are
labelled:
Set 1: NC1 - Normally closed
C1 - Common
NO1 - Normally open
Set 2: NC2 - Normally closed
C2 - Common
NO2 - Normally open
Relay warning
CAUTION: External circuits (such as signal circuits) with
accessible parts or basic insulation only, MUST NOT be
connected to the relay if the relay is also connected to external
circuits which are hazardous live (mains circuits).
(iv) The Sensor connections are labelled “1”, “E” for the
receiver crystal and “2”, “E” for the coax cable to the
transmitter crystal. The screens of these coax cables are
connected to the terminals marked “E”.
(v) The Auxiliary Input is a terminal which can be connected
to a “push to reset” button to achieve a latching alarm, or to
another Mobrey control unit, to give a pump control from the
MCU200 unit relay output. If a short circuit is connected
between terminals 3 & 4, the MCU200 relay, once deenergised, is held de-energised. Even if the sensor attached
to the MCU200 changes state, to that which should energise
the output relay, this relay will not energise until the link
between terminals 3 & 4 is broken in the circuit external to
the MCU200. See section 3.3.
Fig. 5
MCU201 PC Board
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