HF scientific CLX Online Residual Chlorine Monitor (Old) - Manual (Page 16)

CLX (9/07) Page 10
REV 3.1
The connection block is marked N for Neutral and L for line the third symbol
indicates a secure earth ground. The green removable terminal block is suitable for
wire gauges 18 to 12 AWG.
4.4.2 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. Set-up of the RS-485 is covered in 7.3
Configuring the RS–485 Port
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 beside this termination on the PC board.
The recommended cable is 22 AWG shielded twisted pair. The grey terminal block
is removable to assist in making connections.
4.4.3 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 CLX and in a non-alarm condition.
Operation of these alarms is covered in section 7.4 Configuring the Alarms.
The lever operated terminal blocks are rated for wire gauges 28-14.
4.4.4 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. Transformer isolation is provided on the CLX. Do not run 4-
20 mA cables in the same conduit as power. Operation of this output is covered in
section 7.1 Setting the 4-20 mA.
To prevent damage to the instrument, and for general safety ensure that power is
disconnected to the CLX prior to making any connections. For ease of connecting,
remove the plug in terminal block. Polarities of the connections are labeled beside
this termination on the PC board.
The recommended cable is 22 AWG shielded twisted pair. To prevent ground
loops, connect the shield at either the CLX or at its destination, but not both. The
grey terminal block is removable to assist in making connections.
4.4.5 RS-485/4-20 mA cable Ferrite
To meet IEC requirements for RF radiated immunity a clamp-on type ferrite is
supplied. It should be placed on the RS-485 or 4-20 mA cable outside, but as close
as possible to the CLX. If both outputs will be used, an additional ferrite will be
needed and can be ordered from HF scientific inc.