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Basic operation
Temperature
The thermistor-type temperature transducer mounted within the flow meter is in contact
with the oil flow, and temperature is displayed on the left-hand side of the digital display.
Temperature from the remote flow meter plugged into the side of the unit is displayed in the
INT and TACH position; temperature from a remote flow meter plugged into the EXT socket
on the front is displayed in the EXT position. Pressing the °C/°F button toggles the display
between Centigrade and Fahrenheit; the unit selected is indicated by a cursor arrow.
Flow Block - OTC 4291 and/or OTC 4290
The flow comprises an axial turbine mounted in an aluminum block. The oil flow rotates the
turbine and its speed is proportional to the oil velocity. The revolutions of the turbine are
measured by means of a magnetic sensing head which feeds a pulse every time a turbine
blade goes by, to an electric circuit. The circuit amplifies the pulse, shapes it into square wave
form and has a digital output which is directly proportional to the number of pulses per second.
Flow rate is displayed in the right-hand side of the digital display when INT or EXT are selected.
Pressing the units button switches the display to lpm, IMP gpm or US gpm and the selection
is indicated by a cursor arrow. When the flow rate falls below the minimum allowable, "L" is
indicated on the display. When flow rate exceeds the maximum, "H" is indicated on the display.
Loading Valve - OTC 4291 only
All loading valves work on the same theory - a poppet is moved in and out of a flow port via a
threaded shaft. The unique design of the pressure-balanced poppet ensures low handle effort
throughout the flow and pressure ranges in addition to excellent tactile feedback, regardless
of flow direction. In the event of overpressure, replaceable burst discs (situated within the
poppet) rupture, to internally bypass the oil at low pressure.
Pressure Gauge
The pressure gauge has a spiral Bourdon tube and the gauge case is filled with glycerine to
ensure good dampening on pulsating pressures. The gauge is connected to the flow meter
via a micro-bore hose.
Fast Button
The fast button changes the update time of the display. In some situations quick response to
flowrate changes is required. With the cursor arrow highlighting the fast position, the update
time is approximately 1/3 second. Otherwise the update time is approximately 1 second.
When using the fast update, the display will be less stable on flow and shaft speed.
ON Button
The unit is designed to turn off automatically after approximately 15 minutes to conserve
power. When this occurs, user-programmed values are retained in the memory. The unit is
restarted by pressing the ON button.
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