User Manual
MEAS LT Level & Pressure Transducer User Manual
Measurement Specialties, Inc.
www.meas-spec.com
1-757-766-1500
1000 Lucas Way, Hampton, VA 23666 USA
22 of 31
1-800-745-8008
Maximum Cable Lengths and Minimum Supply Voltage
The maximum length of cable to be used with our submersible transducers is largely dependent upon
the type of electrical output of the transducer. For a 0-5 VDC output, a maximum cable length of 100
feet (30 m) is recommended. A voltage output is more susceptible to electrical interference than a 4-
20 mA signal. A 4-20 mA signal can be transmitted much longer distances, depending upon such
factors as temperature, wire size, length of the wire, power supply, and voltage requirements of any
devices to be powered. At 25ºC the 22 AWG conducting copper wire used in our polyurethane
jacketed cable has a resistance of 16.45ohms per 1000 feet (304 m).
Using Ohms Law (E=IR) where E=voltage, I=current and R =resistance, one finds that a 20 mA signal
requires .329 volts to drive it along 1000 feet (304 m) of 22 AWG copper wire (E=16.45 x .020). This
drop is seen on both the supply and return wire for a total loop voltage drop of 0.658 volts
To find out how much voltage is required to drive our MEAS LT submersible level transducer's 4-20
mA signal 10,000 feet, just add the minimum power requirement of the LT transducer (9 VDC) to the
resistance offered by 10,000 feet (3048 m) of our polyurethane jacketed cable (10,000÷1000 x
.658=6.58). The resulting power requirement is 15.58 VDC (9 + 6.58).
Connect the cable shield (drain wire) to a good earth ground. This will protect the transducer from
