CLX (4/18) Page 10
REV 6.0
4.3.3 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 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.
4.3.4 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. 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. 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.
The 4-20mA is factory calibrated. An adjustment is available on the 4-20mA in
sections 7.13 and 7.14. In addition to making adjustments, these menus output
continuous 4 mA or 20 mA and can be used as a signal test. Remember that the
configuration mode will timeout after 15 minutes.
4.3.5 RS-485/4-20 mA cable Ferrite
To meet IEC requirements for RF radiated immunity a clamp-on type ferrite is
supplied in the accessory kit. It should be placed on the RS-485 or 4-20 mA cable
outside 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 Catalog number
24560.
4.4 Installing Reagents
The CLX will require that two reagents be installed prior to operation. These are a buffer
and an indicator. Be sure the correct, prepared reagents are on hand as different reagents
are required to read Free than Total chlorine residual. For reagent preparation refer to
section 10.3 Replacing and Installing the Reagents.
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