Can the CL17 analyser be used to control a chlorine injection pump?

Document ID

Document ID TE5888

Published Date

Published Date 21/01/2019
Question
Can the CL17 analyser be used to control a chlorine injection pump?
Summary
Simple chlorination control using the CL17 analyser.
Answer
Simple Chlorination Control Using the CL17 Analyser
 
When chlorine concentration may be allowed to fluctuate between an upper and lower control limit, the analyser's concentration alarms may be used to provide control, without the need for a more expensive and complex proportional control system.
 
Example circuits are presented in this article.  Figure 1 shows the simplest means of connecting the control circuit.  This circuit may be used with either the 44180 analyser or the new 46780 EC-compliant analyser.  Figure 2 is an alternate circuit which makes use of the failsafe System Alarm in the 46780 analyser.  Figure 3 shows a "failsafe" circuit for use with the 44180 analyser.
 

Figure 1 - Chlorination control using the CL17
 
Note an external contactor or relay (C) is needed, with two normally-open contact pairs (Cl and C2). Alarm1 and Alarm2 are the CL17's built-in alarm relays.  This circuit turns on the chlorine pump when sample chlorine concentration drops below the Alarml set-point; the chlorine pump continues to run until sample chlorine concentration is increased to the Alarm2 set-point.  When the Alarm2 set-point is reached, the pump turns off until sample chlorine concentration falls to the Alarm1 set-point, at which time the cycle is repeated.
 
Alarm2 must be configured as a high alarm; Alarml must be configured as a low alarm.
  
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For example: if you need to control chlorine concentration between 0.5 mg/l and 1.0 mg/l, use the CL17 keyboard to setup Alarm1 at 0.5 mg/l (as a low alarm), and set Alarm2 at 1.0 mg/l (as a high alarm).  If sample chlorine fills below 0.5mg/l, Alarm1 is actuated; this applies power to the contactor which latches "on" (through contacts C2) and applies power to the chlorine pump (through contacts Cl).  The contactor remains latched as chlorine concentration increases above
0.5 mg/l, though Alarm1 is no longer active.  When the chlorine concentration reaches 1.0 mg/l, Alarm2 is actuated, which removes power from the contactor; this also removes power from the chlorine pump. The chlorine pump remains "off" until the chlorine concentration again falls below 0.5 mg/l.
 

Figure 2 - Chlorination control using System Alarm to prevent chlorination in case of analyser fault condition (for 46780 analyser only).
 
The drawing above (figure 2) shows the same control circuit, but with the addition of the CL17's active System Alarm.  (This drawing applies only to the 46780-00 EC compliance version of the CL17.)  In case of loss of power to the analyser, or the occurrence of a System Alarm condition (preventing proper sample measurement), the chlorine pump cannot become latched "on", resulting in uncontrolled chlorination of the sample.  This circuit also actuates an annunciator to alert the operator of a fault condition.
 
The 44180 CL17 analyser (pre-compliance version) can also be used in a similar "failsafe" control configuration, though loss of analyser power will not provide a System Alarm or prevent possible latching "on" of the chlorine pump.  If a 44180 is to be connected as shown in figure 2, System Alarm NO and NC contacts must be reversed.) 
 
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An alternate method of control is shown in figure 3 (below); this assures failsafe operation of the control circuit with a 44180 CL17 in case of analyser power loss or malfunction.  The circuit shown in figure 3 does not provide a System Alarm in case of control failure.
 
When connected as shown in figure 3, Alarm1 must be set as a low alarm at the minimum desired set-point, and Alarm2 set as a low alarm at the maximum desired set-point.  Loss of analyser power (or analyser malfunction) will prevent the chlorine pump from latching "on".
 

Figure 3 - Alternate method of "failsafe" chlorination control using the 44180 CL17