HF scientific MicroTOL Online Turbidimeter - Manual (Page 14)

MICRO TOL (5/10) 8
Rev. 4.8
Figure 5: Electrical Connections for the Instrument
3.3.1 Power: The instrument is equipped with a 100-240 VAC, 47-63 Hz switching power
supply; please verify that the line voltage falls within these specifications. It is
recommended that a circuit breaker be placed prior to the power connection to allow for
service. While making connections, refer to Figure 5. The Micro TOL is not supplied
with a power cord.
3.3.2 RS-485: The RS-485 half-duplex (2-wire) digital interface operates with differential
levels that are not susceptible to electrical interferences. This is why cable lengths up to
3000 ft can be implemented. The last device on each bus may require terminating with a
120-ohm resistor to eliminate signal reflection on the line. Do not run RS-485 cables in
the same conduit as power.
To prevent damage to the instrument, ensure that power is disconnected prior to making
connections. For ease of connecting, remove the plug in terminal block. Connections are
labeled beneath this termination.
3.3.3 Relays: The Alarm 1 and Alarm 2 relays are mechanical relays rated at 240 VAC
2A. Please note that the relays are labeled NO (Normally Open), NC (Normally Closed)
and C (Common). As these alarms are configured fail-safe, the normal condition is with
power applied to the Micro TOL and in a non-alarm condition. Operation of these alarms
is covered in section 7.5 Configuring the Alarms.
3.3.4 4-20 mA: The 4-20 mA output is driven by a 15 VDC power source and can drive
recorder loads up to 600 ohms. This 4-20 mA output is isolated from line power and earth
ground. Do not run 4-20 mA cables in the same conduit as power. Operation of this output
is covered in section 7.2 Setting the 4-20 mA. Optional transformer isolated outputs are
available as a factory installed option (Catalog No. 21045A).
Note: The installation of the 4-20 mA isolator will render the RS-485 non-operational.
Ensure each instrument is not powered when connecting the 4-20 mA. To prevent damage
to the instrument, ensure that power is disconnected prior to making connections. For ease
of connecting, remove the plug in terminal block. Polarities of the connections are labeled
beneath this termination.