HF scientific MicroTOL Online Turbidimeter old series- 0-1000 NTU - Manual (Page 15)

MICRO TOL (12/04)
Rev. 2.7 9
Figure 5: Electrical Connections for the Instrument
3.3.1 Power: The instrument is equipped with a 90-250 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 your connections, refer to Figure 5. The Micro TOL is not
supplied with a power cord.
Note: Your Micro TOL is equipped standard with a 4-20 mA output and alarm relays. If
the optional RS-485 is installed, the 4-20 mA and the relays are disabled and you
should ignore all references to these items.
3.3.2 RS-485 Option: (Part # 19615) The RS-485 half-duplex (2-wire) digital interface
option 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 every
bus must be terminated with a 120 ohm resistor to eliminate the possibilities of signal
reflection on the line. Do not run RS-485 cables in the same conduit as power.
Ensure each instrument is not powered when connecting the RS-485 line. To prevent
damage to the instrument, ensure that power is disconnected prior to making connections.
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 Programming the Alarms & 4-20 mA(if used).
3.3.4 4-20 mA: The 4-20 mA output is driven by a 12 VDC power source and can drive
recorder loads up to 450 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 these
alarms is covered in section 7.5.3 Setting the 4-20 mA Output (if used). Optional optically
isolated outputs are available.
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.