Introduction Liquitron DC4500 Controller

The DC4500 is a microprocessor-based conductivity controller. It is designed for use in a variety of water treatment applications requiring precise control of totally dissolved solids and chemical feed. Among its many uses, the DC4500 will control conductivity and chemical feed in cooling towers and closed loop systems.

LMI’s DC4500 Series of conductivity controllers allows the greatest programming flexibility for cooling tower system applications. This is accomplished through the use of an extensive options menu that is easy to use.
BLEED or BLOWDOWN of system water by valve control can be based on several setpoint options:

  • Conductivity setpoint
  • Hysteresis delay (lower than setpoint) to avoid valve operation chattering
  • Rising or Falling conductivity trip points

FEED of chemical (inhibitor) can be based on four (4) different methods and the pump control can be either On/Off or externally-triggered Variable Speed.

  • FEED at the same time system BLEEDS (lockout timer limits maximum FEED time)
  • FEED time calculated as a percentage of total BLEED time
  • FEED based on a timed cycle (pump is on for a percentage of this timed cycle)
  • FEED based on flow meter input

DUAL BIOCIDE chemical addition may be accomplished by the use of two (2) individually programmable relays or optocoupler outputs. These outputs provide control of two individual chemical addition pumps based on the following options:

  • On/Off or externally-triggered Variable Speed pump control or BOTH for two pump/TIMER operation
  • 28-DAY programmable timer (1, 2, 3, or 4 week selectable cycle)

ALARM indicators and relay outputs are energized based on the following conditions:

  • HIGH conductivity set point is reached
  • LOW conductivity se tpoint is reached
  • NO FLOW condition exists (flow switch must be installed)

The display is a 16-character backlit LCD (liquid crystal display) which is visible in all light conditions. A three-key position membrane is used to enter data and settings (see Figure 1). The conductivity range is 0 – 20,000 µSiemens. The units can be either µSiemens or PPM/TDS (total disolved solids).

All setpoints and parameter settings are retained permanently in a special nonvolatile computer chip memory, preventing their loss due to a power outage. This nonvolatile memory chip allows the unit to be programmed before installation. No battery powered backup is required. Built in test circuits are provided to test each individual relay output wiring and to allow for quick field service isolation of faulty probe, circuit cards, pumps, or solenoids for ease of troubleshooting. A display for temperature is also provided. The range is 32° F to 158° F [0° C to 68° C]. The display can be either fahrenheit or centigrade. This reading also provides the basis for temperature compensation which is performed in all modes.

Liquitron Display Descriptions
Click diagram to see larger image

An analog data (or control) output is provided. This is a non-isolated 4 – 20 mA signal. The conductivity reading that corresponds to minimum and maximum analog signals is fully adjustable. This signal can be used to power chart recorders or other pumps and devices.

The controller operates in two (2) distinct modes, ‘SYSTEM RUN’ and ‘SYSTEM START-UP’ or ‘PROGRAMMING MODE’. The unit will be in the ‘SYSTEM RUN’ mode when it is first turned on. The various program screen menus are used to calibrate the unit, set the control and alarm points, set the inhibitor feed operating parameters, program the biocide [two (2) chemical addition] pumps, and manually test the relays and wiring connections.

In the ‘SYSTEM RUN’ mode the DC4500 monitors the conductivity and activates the appropriate control or alarm relay as necessary based on the set points entered in the ‘SYSTEM START-UP’ mode.

The DC4500 is packaged in a NEMA 12X, flame-retardant, molded TPE enclosure. When ordered, 115 VAC units come fully wired to include input power cord and relay output pigtails to allow for simple installation. The unit can be hardwired through conduit to the lower junction box portion of the enclosure when required. Hard wiring makes the unit suitable for NEMA 4X applications.

2.0 Installation