Babbitt Liquid Level Gauge - Manual (Page 15)

LT-1/LT-2 2-WIRE TRANSMITTER
DESCRIPTION
The LT-1 Level Transmitter is designed for use with the LG Series Level gage to provide a
4-20mA control signal proportional to level. The transmitter consists of a sensor tube made up
of a string of resistors and magnetically operated reed switches. There is a switch and resistor
every ½ inch or ¼ inch along the length of the sensor tube.
The circuit board containing the resistors and switches may be the same length as the
measured range or any portion thereof. The sensor circuit in enclosed in the stainless steel
sensor tube. A threaded connection at the top of the tube is for mounting the transmitter
housing. This housing is rated for Class 1, Division 1, Groups C & D hazardous areas. The LT-1
assembly may be made intrinsically safe by remote mounting of the transmitter in a safe area
and operating the sensor through an approved safety barrier.
As the magnetic float inside the gage chamber rises with increasing fluid level, the switches
close, thereby changing the resistance in the circuit. A two-wire transmitter converts this
resistance change to a 4-20mA current signal corresponding to fluid level. Resolution of the
transmitter is ½ inch (proportional to the spacing of the sensor switches).
SPECIFICATIONS
SENSOR TRANSMITTER
Length Up to 20 Feet Output 4-20mA
Resolution ½ inch LT1-4/20-L-1/2 Power 24 VDC Nominal
¼ inch LT1-4/20-L-1/4 Load 750 Max
Housing 304 Stainless Steel
Operating Temp. to 500°F (Process Fluid)
LT1 CALIBRATION AND TROUBLESHOOTING
USING FLOAT IN LEVEL CHAMBER
A quick check of the calibration is accomplished (with gage mounted) by draining the level
chamber, checking the mechanical zero and then adjusting the sensor tube up or down until it
reads 4mA. Refill the gage chamber or fill it to a point that corresponds to the top range of the
transmitter. The output should now read 20mA.
If a complete calibration is to be performed, remove the transmitter and sensor tube from the
level gage and follow the steps below:
1. Normal operation/Dip Switch 1,2,3 OFF 4 ON
2. Place magnet (float) at 0% (or 4mA mark) on sensor tube.
3. Adjust P2 to Read 4mA on 24 VDC current Loop