Myron L 729II - Manual (Page 27)

B. 4A/4AO MODULE (4-20mA OPTION)
Available only on the digital models 728II, 729II, 723II and
724II, or analog and digital OEM.
-4A 4-20mA Self/Remote-powered Isolated output module
ordered with Monitor/controller.
4AO 4-20mA Self/Remote-powered Isolated output module
ordered separately (includes harness).
1. DESCRIPTION
The 4-20mA option gives the Series II Monitor/controller the
ability to send a signal very long distances with minimal
interferences and signal degradation. The output is an Isolated 4-
20mA signal that corresponds to the full scale range of the
Monitor/controller into which it is installed. This output is easily
configured to be either self-powered or remote-powered as
required for your particular application.
NOTE: The maximum impedance of the user’s current sensor
should not exceed 400 ohms.
Since the output is an isolated current loop, it is the ideal choice
for applications requiring; a control signal to be run very long
distances, systems requiring a 4-20mA input or in instances
where isolation is necessary.
As the output is isolated, and a current, it is useful for long
distance interface, especially where wiring resistances may be
high, and/or the ground potentials may differ between the sensor
input ground and the current receiving instruments ground.
The 4-20mA output will not be degraded in accuracy even when
the ground differences are as much as 120VAC @ 60Hz.
Interface wire resistance of 350Ω will not degrade the accuracy of
the output when interfaced to a typical 250Ω input impedance of a
transmitter current input device.
The output is capable of driving a minimum of 600Ω worst case,
therefore, will satisfy virtually all modern interface requirements.
Current input devices usually have an input impedance of 250Ω,
however, some older designs can have as high as 500Ω or as low
as 10Ω. This “-4A” option will drive any impedance from 0 to 600Ω
without any degradation of performance.
There are two modes in which current loop transmitters operate;
Self-Powered and Remote-Powered.
Self-Powered — the transmitter provides the power to drive
the 4 to 20 mA current. See figure III.B.1.
Remote-powered — the receiving instrument provides the
power to drive the 4 to 20 mA current. See figure III.B.2.
Specifications
Self-Powered and Remote-Powered
Drive Impedance — 0 to 600Ω
Common Mode Maximum — 120VAC @ 60 Hz
Isolation — 100pf max. to Model 750II circuit common
100pf max. to input power line
Calibration
Two multi-turn pots — Factory Set.
4mA = Zero (0)
20mA = Full Scale
Calibration is NOT required. However, if you feel you must verify
or recalibrate, see Recalibration below.
2. INSTALLATION
Briefly -
The 4-20 Module replaces the plastic display retainer plate
attached to the front panel.
The 4-20 Module harness is attached to the main circuit board as
marked ‘4-20’. See figure III.B.4.
The 4-20 output is wired as required - Self-powered or Remote-
powered. See figures III.B.1 & III.B.2.
WARNING: BEFORE STARTING, IF MONITOR/
CONTROLLER IS INSTALLED, ENSURE THE POWER
IS OFF. FAILURE TO DO SO COULD CAUSE DAMAGE
TO THE INSTRUMENT, AND COULD BE HARMFUL OR
23
Figure III.B.1
(+)
(-)
+
-
(+)
SIGNAL OUT
POWER OUT
+
Self - Powered
CURRENT INPUT INSTRUMENT N
Figure III.B.2
(+)
(-)
+
-
(+) SIGNAL OUT
POWER OUT
POWER IN +
Remote - Powered
CURRENT INPUT INSTRUMENT
+ 35 VDC
MAXIMUM
N
POWER IN
SO
P
O
P
I
SO
P
O
P
I
!
CAUTION - READ FOLLOWING CAREFULLY