Signal output
The 4-20 mA signal current output can be used for event recording or
to expand the control facilities for additional relay contacts. This output
can be wired directly to a computer interface without causing earth loop
problems. Correct polarity wiring is essential.
The current signal can also be configured to drive a metering pump with
a signal input. (See Fig. 9)
F
Correct polarity has to be observed when connecting the 4-20mA signal
output.
Electrodes
The co-axial cable used to connect the electrode to the PMH-2 must be
of the type supplied with a carbon sleeve between the centre core and
shield as any standard co-axial cable will cause a very erratic reading. An
impedance converter must be used if the location between electrode and
controller exceeds 10 meters. Special consideration also must be given
when placing an electrode in a treatment bath or pool. The point of injection
of neutralising agent and placement of the electrode (distance between
them) largely determines the dosing characteristics of the PMH-2.
F
Only use special co-axial cable to connect a pH electrode to the PMH-2.
Starting up the Instrument.
After you have installed the instrument and checked all the wiring and
connections open the isolation valves to the sensor to allow water flow
across it. Plug the power cord into the supply and switch on the PMH-2.
The “RUN/CONFIG” LED will light up green and the digital display shows
the measured input value.
F
To quickly change the setpoint push and hold down the encoder until the
green LED flashes and the present setpoint is displayed. Release and dial
a new setpoint. Push again until the SAVE LED flashes two times.
PMH-2 Instruction manual
PAGE 11
