DIGITAL LOOP POWERED INDICATOR
JM-408
PRINCIPLE OF OPERATION
The Model JM-408 Digital process Indicator is a compact, rugged and reliable indicating instrument
which is specifically designed for accurate process measurement applications in areas without
power availability.
The Indicator accepts an industrial standard current input signal of 4 to 20 mA DC and displays the
actual process value calibrated in the desired units, on a linear scale. The process value is
displayed on a 4-Digit seven-segment red LED digital display module. There is no necessity of any
external Power Supply.
The instrument is fully configurable and can be calibrated on any scale range from
999 to +9999
units. Decimal Point setting is also provided in the instrument.
The principal of operation is briefly as follows :- The Input signal is passed through a series of
amplification and conditioning stages. Initially, the signal is conditioned internally and fed to a
signal convertor circuit. Thereafter, the transduced signal output of this convertor is fed into an A/D
Convertor before being finally passed through a Decoder/Driver digitizing circuit which displays the
input signal in the form of decimal digits on a seven-segment display module.
The field mounted unit has no potentiometers to adjust and all settings can be performed digitally
using only the three membrane switches that are available on the front panel. The NEMA4X rating
provides total immunity to corrosive atmospheres, high humidity (including condensation) and dust.
The JM-408 Indicator is therefore an ideal single unit substitute to conventional analog indicators
because of it’s easy set up procedure and inherent accuracy in process control, besides other
superior characteristics like immunity to Shocks, Dust, Ambient temperatures, Humidity and
Corrosive atmospheres. It’s main advantage is that it is completely current loop-driven, eliminating
the requirement of any external power supply source and associated cabling.
The instrument is manufactured using selected high-grade components which guarantee its
reliability and long operational parts. There are no moving parts and no potentiometers that may
drift over time and in high vibration applications.
INSTALLATION
The Model JM-408 is designed for field mounting in an Aluminum die-cast enclosure with IP65
ingress protection. The instrument should be first installed on the required panel face by means of
the two clamps provided for the same.
All inter-connections to the instrument should be made with strong multi-strand wire of the order of
2.5 sq.mm. The ends of the wires should be properly ferruled and suitable lugs must be used for
effective termination. The Cables carrying the Input Signal should be properly isolated from the
Power Line cables (even separate router channels), to prevent any electromagnetic interferences
in the Input Signal readings from disturbances in the Mains Power Line. There is no requirement of
power supply or earthing. It is recommended that the polarities of the input signal be double-
checked for correctness before energizing the instrument.
