LTH MOD53, Operation Manual

Page: 56 / 110

9 Current Output
55
DUAL CURRENT OUTPUTS
If the instrument is supplied with two current outputs they are designated A & B
respectively. The menu for current output B is identical to A and is displayed after
the A menu.
PROPORTIONAL CONTROL
Many devices such as motor speed controllers, valve actuators, or stroke
positioners will accept an analogue 4-20 mA control signal.
It is possible to use the measurement signal from the instrument as a control
signal. By setting the point at which the output is 4 mA as the set point (e.g. 7.00
ppm) and the point at which the output is 20 mA as the proportional band (e.g. 4.00
ppm) a simple form of proportional control is achieved. If this signal was used to
drive a valve actuator, the valve would be fully open at 4.00 ppm; half open at 5.50
ppm and closed at 7.00 ppm.
ERROR CONDITION
The current outputs can be programmed to output 22mA or 0mA when an error is
detected on the source (i.e. Sensor Fault, Temperature Over or Under Range), to
provide remote warning of error conditions or to ensure fail safe operation. The
default state of is disabled, where the parameter is set to ”
No ”.