Chlorine level monitoring

Jim-

I would check with your local HACH representative (or the mfr. you currently use). Their chlorine analyzer should be capable of sending a 4-20 mA signal which could tie to your make shift alarm.

Regards,
Brad Castleberry
bcastleb@hdrinc.com

I am a trustee of a small water system. We want to monitor the chlorine level in our intake tank. The idea would be that some kind of a probe in the tank. If the level dropped below 0.3 ppm or rose above 0.6 ppm, then a switch would close and set off an alarm. We have the alarm system based on a modified walkie talkie. The problem is what kind of equipment would be necessary in the tank. The system is "up in the hills" so, as much as possible, it should stand alone.. no fancy equipment which requires monitoring. the probe can be mounted at the ooutflow end of the tank so that there would be a constant flow of water.

Thanks
Jim Lewall

Jim,

There are lots of options for selecting a chlorine monitoring system. The Hach CL-17 (800-227-4224) uses a DPD method for chlorine analysis, so there are bottles of chemicals to replace every month or so. There are a number of amperimetric electrode units also available from companies like ATI (800-959-0299), Great Lakes Instruments (414-355-3601), and Rosemount. These units have to be calibrated every 5-7 days (from our experience) and the electrode membranes replaced every few months. All of these options come equipped with alarm relays, require 120 VAC, use a small sidestream flow (about 1 lpm) that must be wasted, and cost between $2,500 - 3,500.

Another possibility is to use an ORP probe instead of a chlorine analyzer. You would have to run lab tests to correlate ORP levels in millivolts with chlorine levels in mg/L. Stranco (800-882-6466) sells a high-performance ORP monitoring system whose cost is similar to that of the chlorine analyzers. A cheaper system is available from Cole-Parmer (800-323-4340) for about $375 (see page 631 of their catalog). We have had mixed success trying to use ORP as an indicator of residual disinfectant. Each manufacturer's probe seems to respond differently and in general, they are slow to respond to step changes in chlorine levels. Most people in the water industry don't believe in using ORP to monitor chlorine levels.

Hope this helps.
Lew Rossman