HF scientific AccUView Wastewater UV %Transmission Monitor - Manual (Page 15)

SENSOR TERMINAL BOX
POWER SUPPLY
TERMINAL BLOCK
ALARM
TERMINAL BLOCK
240 VAC, 2A
4-20ma / RS485
TERMINAL BLOCK
POWER CABLE
STRAIN RELIEF
(WITH LID REMOVED)
PUMP
TERMINAL BLOCK
12 VDC
Figure 7: Sensor Terminal Box
3.3.2 RS-485 (optional): The connection for the RS-485 may be made in the sensor
terminal box (see figure 7). The RS-485 Modbus or special protocol half-duplex (2-wire)
digital interface operates with differential levels that are less 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.
This factory installed option is available (HF catalog #19851A). Please note that adding
this option deletes the standard isolation on the 4-20 mA output.
3.3.3 Relay: Connections for the relay are located in the sensor terminal box (see figure
7). The Alarm relay is a mechanical relay rated at 240 VAC 2A. Please note that the relay
is labeled NO (Normally Open), NC (Normally Closed) and C (Common). As this alarm is
configured fail-safe, the normal condition is with power applied to the AccUView
Wastewater and in a non-alarm condition. Operation of this alarm is covered in section 7.4
Configuring the Alarm.
3.3.4 4-20 mA: Connection to the 4-20 mA is made inside the sensor terminal box (see
figure 7). The 4-20 mA output is driven by a 15 VDC power source and can drive recorder
loads up to 600 ohms. 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. The outputs are equipped
standard with an installed looped powered isolator (500V isolation).
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. Polarity of the
connections is labeled beneath this termination.
AccUView Wastewater (1/09) 9
Rev. 2.9