Hardy HI 2204LT Weight Transmitter - Manual (Page 11)

HI 2201LT/HI 2204LT
7
Precautions on
Grounding 1. Do not connect the signal return to the earth
ground at more than one point in the output/
power loop.
2. Any receiver or electronic device inserted in the
output/power loop must be designed so that the
connections to the loop are isolated from ground.
NOTE: Only the one point where the loop is already grounded
can accept a grounded lead.
3. Do not connect the earth ground to the signal
return in the transmitter input circuit.
4. Do not connect any of the transducer signal wires
to the earth ground.
Isolation The AC power sources for this instrument must be
separate and isolated from the power supplied to any
switches, relays, solenoids, or motors which can intro-
duce excessive noise into the instrument’s circuits.
Load cells and load cell signal wires are not typically
grounded, and they are not typically connected to
their shields or to the load cell case. If the recommen-
dations given in the grounding and shielding section
are followed, there will be no need for isolation in the
transmitter/load-cell circuit. In fact, in the load cell
circuit, isolation adds to the cost and inaccuracy and is
not recommended.
It is generally not necessary to provide isolation in the
output loop. However, when ground-loop problems
do occur, a Loop isolator designed to handle the 4 ma
to 20 ma Loop Powered Level Weight Transmitter
signal may be installed. (See Fig. 5)
Calibration The HI 2201LT Loop Powered Level Weight Trans-
mitter is calibrated at the factory for 4 ma current out-
put with zero millivolts input and 20 ma output for 15
mV input (based on a 3mV/V input source and 5 V
excitation). In most cases, the transmitter will require
a very simple recalibration to the system in which it is
installed. The calibration procedure provided is
designed to be used either in new installations or for
recalibration of existing systems, and will work with 3
mV/V or 2 mV/V load cells. Be sure to read all cali-