HYDROLOGICAL SERVICES ML1-420 - 3.1.3 4-20 mA Transducer Input; 3.1.4 Communications

Hydrological Services Pty Ltd
Data Logger Model ML1-420
© Copyright
ML1-420 100-7 Issue 1.00 6 Apr, 2011
Internal battery
for maintaining
time when no
external power
is present !
ML420
Sense
Brown
4-20mA
Transducer
Green
4-20mA+
12V Battery
-
+
Batt +12V
Batt 0V
4-20mA-
3.1.3 4-20mA Transducer Input
The 4-20mA connection is via 2 wires into a screwless terminal block. The battery voltage is
switched to the 4-20mA transducer and the current is measured across an internal sense
resistor.
Connection of 4-20mA Transducer
3.1.4 Communications
The pinout of the DB9 female connector on the front of the ML1-420 logger is as follows :-
Pin
Connection
ML1-420 Logger Signal Name
DB9 Female
PC Signal
Direction
PC Signal
DB9 Male
1 No Connection CD
2 Tx (RS232 Serial data output) Rx
3 Rx (RS232 Serial data input) Tx
4 External Power (+ DTR / DSR loop) DTR
5 Gnd Gnd
6 External Power (+ DSR / DTR loop) DSR
7 External Power (+ RTS / CTS loop) RTS
8 External Power (+CTS / RTS loop) CTS
9 Contact closure input (See note 3) RI
Notes:
1. When the ML1-420 is directly connected to a PC the following handshake signals are
linked
 Pins 4 and 6 are linked together inside the ML1-420.
 Pins 7 and 8 are linked together inside the ML1-420.