Hydro Instruments 210 Series Manuale utente
Series 210
Amperometric Residual Chlorine Analyzer
Instruction Manual
RAH-210 Rev. 5/12/2021
The information contained in this manual was current at the time of printing. The most current
versions of all Hydro Instruments manuals can be found on our website: www.hydroinstruments.com
1
Hydro Instruments
Series 210 Amperometric Residual Chlorine Analyzer
Table of Contents
I. Functions and Capabilities .....................................................................3
1. Basic Concept Description
2. Galvanic Cell Theory
3. Chlorine Chemistry
4. Measurement Chemistry
5. Basic Specifi cations
II. System Component Description .............................................................6
1. Measurement Cell
2. Temperature Probe
3. Optional Reagent Chemical Feed System
4. Optional pH Sensor
III. Installation ................................................................................................7
1. Sample Water Connection and Control
2. Sample Water Disposal Considerations
3. Sample Point Selection
IV. Setup, Reagents and Conditioning the Analyzer ................................10
1. Reagent Chemical Setup and Requirements
2. Conditioning the Analyzer
V. Calibration and Programming ...............................................................12
1. Modes of the RAH-210 Residual Analyzer
2. Switching Between Modes
3. Operating the Keypad
VI. Explanation of Operation Mode Screens .............................................14
VII. Explanation of Confi guration Mode Screens ......................................16
VIII. Explanation of PID Control Mode Screens ..........................................23
IX. Maintenance & Cleaning ........................................................................25
1. Inlet Filter Screen and Weir
2. Flushing Measurement Cell
3. Reagent Valve (Star Wheel)
4. Cell Assembly
5. Motor Striker Assembly
6. Thermistor
7. pH Probe
X. Troubleshooting .....................................................................................28
XI. Optional Data Logger .............................................................................32
Figures:
1. Hypochlorous Acid Dissociation Curves ..........................................................5
2. Measurement Cell Flow Diagram ....................................................................6
3. Sample Water Piping Diagram ........................................................................8
4. Sample Point Connection Diagram .................................................................9
5. Sample Point Selection Diagram .....................................................................9
6. Operation Menu Flow Chart ..........................................................................13
7. Confi guration Menus from Password 250 .....................................................15
8. PID Control Confi guration Menus from Password 220 ..................................21
9. pH Calibration Menu Flow Chart ...................................................................22
10. RAH-210 Circuit Boards ................................................................................41
11. Monitor Internal Wiring and Connections ......................................................42
Drawings:
Residual Chlorine Analyzer Measurement Cell ........................................34-40
2
I. FUNCTIONS AND CAPABILITIES
1. Basic Concept Description: The Series 210 Residual Analyzer uses a Galvanic measurement
cell consisting of a Cathode and a Copper Anode with the sample water as the electrolyte. This
measurement method is referred to as Amperometric and has been in use for over 50 years.
As described below, the measurement cell can be used to measure the concentration of Free
Chlorine, Total Chlorine, Chlorine Dioxide and other oxidants. Certain chemical species produce
an electrical current in the cell that is proportional to their concentration in the sample water. This
electrical current is read and manipulated by the Series 210 monitor circuit board. The system
employs a motor to continuously clean the measurement cell by the abrasive action of Tefl on balls.
Sample water continuously fl ows through the measurement cell at a controlled rate. A Temperature
sensor is employed to compensate for signal fl uctuations caused by Temperature changes. The
pH of the sample water is either manually entered for pH compensation in the software or else a pH
buff er feed system is used to control the pH in the sample water. If Total Chlorine, Chlorine Dioxide,
or some other oxidants are being measured, then another chemical will be continuously injected into
the sample water prior to its entering the measurement cell.
This analyzer is also equipped with a complete PID Control program, which can be enabled or disabled
as desired. The program accepts a proportional (fl ow) analog 4-20 mA input and uses the residual
value produced by the analyzer. This control program can be enabled as proportional (fl ow pacing),
set-point (residual) or PID (compound loop) control.
2. Galvanic Cell Theory: Pure water has a relatively low conductivity. However, the presence of ionizing
species increases the conductivity. If two electrodes are immersed in a solution containing chemical
species (ions) capable of being reduced (gaining electrons) then this species can move toward
the cathode where it can accept electrons from the cathode. To balance this fl ow of electrons
(current), an oxidation reaction (where an oxidizable species loses electrons at the same rate) must
simultaneously occur at the anode surface.
As the reactions occur at the surface of each electrode, the local concentration of the reducible/
oxidizable species drops, thus creating local concentration gradients. As a result of the
concentration gradients, the process of diff usion moves more of these species toward the
electrodes. The rate at which diff usion moves these species to the electrode surfaces is referred to
as the rate of arrival.
The electrical current produced in the cell is proportional to the rate of arrival of the reducible/oxidizable
species at the electrodes. As the concentration of these species increases, so does the rate of
arrival. Also, as the temperature increases, the rate of arrival increases for a given concentration.
After some temperature compensation, the current is therefore an indication of species concentration.
The current is read by electrically connecting the cathode and anode.
3. Chlorine Chemistry: When Chlorine dissolves in water it forms Hypochlorous Acid according to the
following reactions:
Chlorine Gas: Cl2
Cl
2 + H2O ↔ HOCl + HCl
Sodium Hypochlorite: NaOCl
NaOCl + H2O ↔ HOCl + Na+ + OH–
Calcium Hypochlorite: Ca(OCl)2
Ca(OCl)2 + 2H2O ↔ 2HOCl + Ca++ + 2OH–
3
Hypochlorous Acid is a weak acid that partially dissociates into a Hydrogen Ion and a Hypochlorite
Ion as follows:
HOCl ↔ H+ + OCl–
The degree of dissociation depends on the pH and the Temperature. Regardless of Temperature,
below a pH of 5 the dissociation of HOCl remains virtually zero and above a pH of 10 the dissociation
of HOCl is virtually 100%. Figure 1 shows this dissociation curve at several Temperatures. The sum
of Hypochlorous Acid and Hypochlorite Ion is referred to as Free Available Chlorine.
When Ammonia Nitrogen is present in the water, some or all of the Free Available Chlorine will be
converted into Chloramine compounds according to the following reactions:
NH
3 + HOCl → H2O + NH2Cl (Monochloramine)
NH
3 + 2HOCl → 2H2O + NHCl2 (Dichloramine)
NH
3 + 3HOCl → 3H2O + NCl3 (Nitrogen Trichloride)
The sum of the Chloramine compounds is referred to as “Combined Available Chlorine”. Also, the
sum of Free Available and Combined Available Chlorine is referred to as “Total Available Chlorine”.
4. Measurement Chemistry:
Free Chlorine Measurements: As discussed above, Free Chlorine is the sum of Hypochlorous
Acid and Hypochlorite Ion concentrations. Hypochlorous Acid is a reducible species in the Series
210 Residual Chlorine Analyzer. Therefore the measurement cell can be used to measure the
concentration of Hypochlorous Acid.
This measurement can be used to determine the concentration of Free Chlorine by one of two
methods. Consider Figure 1 in the discussion of both methods.
First, an acidic buff er solution can be injected into the water sample stream to reduce the pH below 5,
so that all of the Free Chlorine is in the form of Hypochlorous Acid.
Second, pH and Temperature measurements can be used to continuously determine the degree of
Hypochlorous Acid dissociation through software. The instantaneous degree of dissociation value
can then be used in conjunction with the Hypochlorous Acid concentration measurement to determine
the Free Chlorine concentration. This method will be referred to as “pH Compensation”.
The reaction at the cathode surface in this measurement is as follows:
HOCl + 2e– → Cl– + OH–
Total Chlorine Measurements: As discussed above, Total Chlorine is defi ned as the sum of Free
Available Chlorine and Combined Available Chlorine. Combined Available Chlorine species are not
reducible in the Series 210 measurement cell. Therefore, the following technique must be employed
to obtain a measurement.
First, Potassium Iodide (KI) is injected into the sample water so that all species comprising Total
Chlorine react to form Potassium Chloride (KCl). The measurement cell then measures KCl
concentration in the same fashion that it can measure HOCl concentration. Since KCl concentration
is proportional to Total Chlorine concentration, the measurement of KCl is also a measurement of
Total Chlorine concentration. The relevant reactions are as follows.
Free Chlorine Residual:
2H + 2HOCl + 2KI ↔ I2 + 2KCl + 2H2O
4
Combined Chlorine Residual:
3H
2O + 2NH2Cl + 2KI ↔ 2KCl + I2 + 2NH4OH + ½O2
2H
2O + NHCl2 + 2KI ↔ 2KCl + I2 + NH4OH + ½O2
5H
2O + 2NCl3 + 6KI ↔ 6KCl + 3I2 + 2NH4OH + 1.5O2
Second, the pH must be reduced to the range of 4.0 to 4.5 in order to prevent any dissociation of the
Hypochlorous Acid or the Potassium Chloride (KCl).
5. Basic Specifi cations
Temperature Range: 0º to 50º C (32º to 122º F).
Sample Water Flow Rate: 500 ml/min (8 gal/hr) ideal
150 ml/min (2.4 gal/hr) minimum
Sample Pressure: 5 psig (0.3 bar) maximum at inlet point.
Sample Supply: Continuous. Electrodes must be kept wet with fresh water.
Speed of Response: 4 seconds from sample entry to display indication.
T
90: Approx. 90 to 120 seconds
T
100: Approx. 10 minutes.
Sample Water: Metal ions or certain corrosion inhibitors may eff ect analyzer operation.
Range: 0 to 0.1 to 0 to 20 mg/l (PPM). Field adjustable.
Power Consumption: 10 W max.
Power Requirements: 120VAC, 50/60 Hz or 240VAC, 50/60 Hz, single phase.
Accuracy: 0.003 mg/l or +/-1% of range, whichever is larger.
Sensitivity: 0.001 mg/l (1 ppb)
Input Signals: (5) Analog 4-20 mA.
Output Signals: (4) Isolated 4-20 mA Analog (Res, pH, Temp, Turbidity, or Control).
Digital Communication: Modbus RS-485 Two-Way
pH Sensor Input: Included.
Temperature Sensor Input: Included (for 10K Ohm thermistor).
Relay Contacts (4): 10 Amps @ 120 VAC or 24 VDC, resistive load, 5 Amps @ 240 VAC, resistive
load.
Reagent Requirements
Free Chlorine (pH Compensated): None.
Free Chlorine (not pH Compensated):
pH Buff er or CO2 gas.
Total Chlorine: pH Buff er or CO2 gas
and Potassium Iodide.
Chlorine Dioxide: pH Buff er and Glycine.
Bromine Chloride: pH Buff er or CO2
gas and Potassium Iodide.
Iodine: pH Buff er or CO2 gas.
P(
(/#L /#L
n
&)'52%
(YPOCHLOROUS!CID$ISSOCIATION#URVES
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5
II. SYSTEM COMPONENT DESCRIPTION
Refer to Figure 2 for this section.
1. Measurement Cell: The measurement electrodes consist of a cathode and a Copper anode. The
measurement electrodes are mounted in a PVC housing assembly. The electrodes are in the shape
of concentric cylinders. The cathode is the inner smaller cylinder and the anode is the outer larger
cylinder. The sample water fi lls the gap in between the electrodes and continually fl ows in the upward
direction. The detailed description of the electro-chemical process can be found in section I.
The Series 210 Residual Chlorine Analyzer also employs a continuous electrode cleaning method.
The purpose of this method is to keep the electrode surfaces clean and free of chemical desposits
to ensure consistent measurement readings. The cleaning is accomplished by fi lling the space
between the electrodes with roughly 130 7⁄32" diameter PTFE cleaning balls and continuously driving
them around the annular gap with a rotary motor. These balls and the electrodes require periodic
maintenance and replacement as described in Section VI.
2. Temperature Probe: A Thermistor is used to continuously measure the sample water Temperature.
The Temperature can be displayed and retransmitted by the Series 210 Residual Chlorine Analyzer.
It is also used in software for signal manipulation for the two following reasons:
Temperature compensation for the effects of Thermal Diffusion: As described in Section I, the rate of
arrival at the electrode surfaces is dependent on the Temperature of the sample water. If the device
is being used at a location with constant water Temperature, then this compensation is not necessary.
However, if the sample water Temperature experiences signifi cant fl uctuations, then the raw signal
will be aff ected and software Temperature compensation is necessary for accurate readings.
For use in pH compensation: As described in Section I, if the pH buff er is not being used to lower the
sample water pH, then pH compensation is necessary to achieve accurate measurements.
3. Optional Reagent Chemical Feed System: The Series 210 Residual Chlorine Analyzer can be
fi tted with a mechanically driven reagent feed system. The chemical reagent solution is continuously
injected at a controlled rate by a mechanical system driven by the motor that is used to drive the
cleaning balls in the measurement cell. Section I.5 outlines the various reagent solutions that may be
needed depending on the target measurement species and the measurement method. If operating
properly, the reagent feed system should feed the solution at a rate of 3⁄4" to 11⁄8" (20 to 30 mm)
level change in 24 hours.
4. Optional pH Probe: If the unit is not fi tted with the reagent feed system then it is recommend that
the unit be equipped with an external pH probe. This probe is mounted in its own acrylic chamber
located to the right of the measurement cell and used used to compensate for the eff ects of pH
as described in section I. It is not recommended that this compensation method be used where
the sample water being measured is consistently above pH 8.5. Should this be the case Hydro
Instruments recommends utilizing the reagent feed system.
FIGURE 2
Motor
Water
Sample
Inlet
Cleaning
Balls
Rotating
Striker
Cylindrical
Copper
Electrode
Probe
Screen
Drain
Electrical
Signal
Overflow
to Drain
Rotary Valve
Buffer Chemical Feed
6
III. INSTALLATION
Refer to Figure 3 for this section.
1. Sample Water Connection and Control: The following are some considerations relating to the
sample water supply. The Series 210 Residual Chlorine Analyzer requires a constant supply of sample
water at a controlled rate and pressure. Precautions should also be taken to ensure that the sample
water reaching the measurement cell is not altered as it passes through the sample water piping. Also,
the connection to the sample point should be made in such a way to avoid receiving air or sediment
from the pipe. Consider fi gure 4 when creating your sample water line
Flow: As mentioned in the specifi cations in Section I, the sample water fl ow rate should be
controlled at 500 ml/minute (8 GPH). A fl ow meter and rate control valve may be necessary to
achieve and maintain this fl ow rate. This can be installed upstream from the measurement cell.
Pressure: Where the sample point has a water pressure higher than 5 psig, a pressure-reducing
valve must be employed to deliver the sample water to the measurement cell. The sample water
entering the measurement cell should be at a pressure below 5 psig. If the sample point pressure
is too low, then it may be necessary to use a sample pump to deliver the sample water to the
measurement cell.
Other Considerations: It should be considered, that any biological growth inside the sample
piping system will have some chemical demand. This can cause the sample water reaching the
measurement cell to not be an accurate sample. For example, the chlorine residual could fall as the
sample water passes through the sample water piping system. For this reason, it may be necessary
to periodically disinfect the sample water piping system to prevent any biological growth. Also, it is
generally not recommended to use a fi lter in this piping system because as the fi lter collects particles it
will develop a chlorine demand and therefore, the chlorine residual in the sample water will be reduced
by the fi lter, leading to inaccurate readings. However, in certain installations with signifi cant amounts
of solids in the sample water (particularly iron and manganese) the use of sample water fi lters may be
necessary.
2. Sample Water Disposal Considerations: If no reagent chemical is being injected, then the disposal
of the water departing the measurement cell is usually not a signifi cant concern. However, if some
reagent chemicals are being injected, then all applicable regulations should be considered before
making the decision of how and where to dispose of the wastewater exiting the measurement cell.
Refer to the MSDS of the chemical in question for instructions on proper disposal.
3. Sample Point Selection: Consider Figure 5 for this section.
There are at least two general concepts to consider when selecting the sample point location. First, is
to select a point that allows reliable determination of the chemical residual concentration at the most
critical point for the particular installation. Second, is to take into consideration the chemical injection
control timing. A balance between these considerations must be reached.
Each system is unique, however in general the goal of the chemical injection is to achieve some result
by maintaining a certain chemical residual concentration at a particular point in the system. For
example, to maintain a specifi c chlorine residual at the exit of the drinking water facility. The location
should be selected so that the injected chemical is already fully mixed so that an accurate sample can
be sent to the measurement cell.
WARNING! Do not run analyzer without sample water running through! Lack of,
or interruption of water fl ow to analyzer cell can overheat the motor and cause
premature failure.
7
FIGURE 3 (Sampling Examples)
Sample
Pump
Low Pressure
Sample Water
Source
Flush Valve
to Drain
Pressure entering
RAH-210 must be
reduced to 5 psig
(0.3 bar) or less
Sample Water
Flow Meter
Y-Strainer Pressure Reducing
Valve Assembly
Pressure Reducing
Valve Assembly
Grab
Sample
Valve
To Drain
Pressurized
Sample Water
Source
It should also be considered that the sample point should be located such that the residual
reading can be used as a control signal for the chemical injection. Especially, it should be
considered that if there is a long time delay between chemical injection changes and the
change being detected by the measurement cell, then chemical injection control is adversely
aff ected. The delay time should be kept as short as possible. We recommend that the time
be less than 5 minutes.
8
!IR
3EDIMENT
!IR
3EDIMENT
!IR
3EDIMENT
!IR
3EDIMENT
0//2 0//2
'//$ "%34
FIGURE 4 (Sample Sources)
FIGURE 5 (Installation Example)
TRUE
BLUE
TRUE
BLUE
TRUE
BLUE
40
80
100
140
180
200
40
80
100
140
180
200
40
80
100
140
180
200
40
80
100
140
180
200
Min. = 10 x Dia.pipe
Ideal = 20 x Dia.pipe
Residual Signal (4-20mA)Water Flow Signal (4-20mA)
NET #1 = 1234
NET #2 = 5678
Residual Chlorine Analyzer
RAH-210
Wall Panel Omni-Valve
Vacuum Regulator
Ejector
Sample Water PRV
RAH-PRV
Corporation Stop
Vent
9
IV. SETUP, REAGENTS, & CONDITIONING THE ANALYZER
IMPORTANT NOTE: Prior to starting the analyzer, turn the striker with your thumb (from left to right) to
be sure the motor turns freely. If the motor becomes stuck or is diffi cult to turn by hand, the problem
must be identifi ed and corrected prior to starting the analyzer. See Section X (Troubleshooting).
1. Reagent Chemical Setup and Requirements: This section pertains to systems using the reagent
feed system. The following explains what reagents are to be used depending on the measurement
method.
a. Free Chlorine with pH compensation in software – No reagents required.
b. Free Chlorine without pH compensation – Requires pH buff er solution.
c. Total Chlorine – Requires pH buff er and potassium iodide.
d. Chlorine Dioxide – Requires pH buff er and glycine.
e. Bromine Chloride – Requires pH buff er and potassium iodide.
f. Iodine – Requires pH buff er.
NOTE: The 2 liter reagent bottle will last for approximately one week of continuous use.
Use of pH buffer: It should be noted that the pH buff er feed system is designed to reduce pH in the
sample cell in order to minimize or eliminate the eff ects of dissociation.
The following pH buff er is recommended:
Sodium acetate trihydrate and glacial acetic acid can be mixed with distilled deionized water as
follows:
a. Add 850 mL of distilled deionized water to a 1⁄2 gallon (2L) bottle.
b. Add 486 grams sodium acetate trihydrate crystals and mix until all the crystals are dissolved.
c. Add 952 grams or 907 mL of glacial acetic acid to the bottle.
d. Fill the bottle to the top with distilled deionized water. Mix thoroughly.
e. If necessary check the pH of the solution (pH = 4). If not, add more acetic acid to lower the pH.
f. To conserve buff er you may also dilute 50:50 with distilled deionized water in a separate 1⁄2 gal (2 L)
container and store the remaining solution for later use. However, please be aware that doing this
will lower the buff ering capacity of the solution.
Use of Potassium Iodide reagent: This reagent is always used together with the above mentioned
pH buff ers. To prepare the combined reagent solution, follow this procedure:
a. Fill a 1⁄2 gallon (2 L) bottle half way with distilled deionized water.
b. Add potassium iodide crystals as follows to the 1⁄2 gallon bottle.
c. Shake the bottle until the crystals are all dissolved completely.
d. Fill the 1⁄2 gallon bottle to the top with the pH buff er solution.
TABLE 1
Potassium Iodide (KI) (grams) Analyzer Range (ppm) (mg/l)
2.65 0 to 0.2
5.3 0 to 0.5
21 0 to 2.0
32 0 to 3.0
53 0 to 5.0
105 10 or 20
10
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