1 Scope
NOTE This specification covers online, continuous-reading analytical instrumentation that measures water-quality and process chemistry parameters in water treatment, wastewater treatment, and industrial process applications. (1.1)
NOTE Equipment covered includes the sensor or measuring cell, the analyzer or transmitter, the sample conditioning and sample-delivery provisions (flow cells, constant-head devices, sample pumps, strainers, and sample panels), any reagents and reagent-handling provisions for wet-chemistry analyzers, the automatic temperature compensation, and the signal output and digital communication interface to the control system. (1.2)
NOTE Both in-situ sensors (insertion or submersible probes mounted directly in the process) and flow-through analyzers (sensors mounted in a sample loop fed from a tap) are addressed. (1.3)
NOTE An online analyzer differs fundamentally from a laboratory bench instrument: it must run unattended for weeks between service visits, tolerate the fouling and temperature swings of the live process, and produce a signal the control system can act on continuously. (1.4)
NOTE A subset of these analyzers serves a regulatory compliance-monitoring role — the reading is reported to the primacy agency to demonstrate compliance with a drinking-water or discharge permit — and those analyzers carry method-specific requirements (USEPA Method 334.0 for online chlorine, USEPA Method 180.1 for turbidity) beyond those of a process-control-only analyzer. (1.5)
NOTE The boundary of work under this standard is the analyzer system from the sample tap (or the insertion point in the process) through the sensor, the analyzer/transmitter, and the output signal at the field terminal. (1.6)
1.7Equipment shall comply with the applicable USEPA-approved method, ASTM test method, or Standard Methods procedure for each measured parameter as identified in this standard.
1.8Analyzers serving a drinking-water or discharge compliance-monitoring function shall comply with the specific USEPA method approved for online compliance use for that parameter.
1.9Electrical and electronic components shall be listed by a Nationally Recognized Testing Laboratory to the applicable UL or equivalent product standard, and analyzers installed in classified (hazardous) locations shall carry the area-classification listing required for the location.
2 Referenced Standards
2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where conflicts exist between referenced standards, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
2.3Where an analyzer serves a compliance-monitoring function, the USEPA-approved method in effect under the applicable regulation at the time of reporting shall govern, and shall take precedence over a general process-measurement method.
| Standard |
Title |
| USEPA Method 180.1 |
Determination of Turbidity by Nephelometry (white-light / tungsten source; drinking-water compliance) |
| ISO 7027-1 |
Water Quality — Determination of Turbidity (near-infrared LED source method) |
| USEPA Method 334.0 |
Determination of Residual Chlorine in Drinking Water Using an On-line Chlorine Analyzer |
| ASTM D1293 |
Standard Test Methods for pH of Water (Test Method B for continuous measurement) |
| ASTM D6569 |
Standard Test Method for On-Line Measurement of pH |
| ASTM D888 |
Standard Test Methods for Dissolved Oxygen in Water (Method B electrochemical; Method C luminescence-based) |
| ISO 17289 |
Water Quality — Determination of Dissolved Oxygen — Optical Sensor Method |
| ASTM D1125 |
Standard Test Methods for Electrical Conductivity and Resistivity of Water |
| ASTM D1498 |
Standard Test Method for Oxidation-Reduction Potential of Water |
| USEPA Method 415.3 |
Determination of Total Organic Carbon and Specific UV Absorbance at 254 nm in Source and Drinking Water |
| Standard Methods (APHA/AWWA/WEF) |
Standard Methods for the Examination of Water and Wastewater — 2130 Turbidity, 2510 Conductivity, 4500-Cl Chlorine (Residual), 4500-H+ pH, 4500-O Oxygen (Dissolved), 4500-NH3 Nitrogen (Ammonia), 4500-NO3 Nitrogen (Nitrate), 4500-O3 Ozone |
| ANSI/ISA-5.1 |
Instrumentation Symbols and Identification |
| ANSI/ISA-50.00.01 |
Compatibility of Analog Signals for Electronic Industrial Process Instruments (4-20 mA) |
| NAMUR NE43 |
Standardization of the Signal Level for the Failure Information of Digital Transmitters (3.6 mA / 21 mA fault levels) |
| HART |
Highway Addressable Remote Transducer protocol (digital data over the 4-20 mA loop) |
| AWWA Standards |
American Water Works Association standards applicable to treatment-plant instrumentation and disinfection monitoring |
| NFPA 70 |
National Electrical Code (NEC) — including hazardous (classified) location provisions |
| UL 61010-1 |
Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use |
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following for the Engineer's review and approval prior to procurement.
- Manufacturer's product data for each analyzer and sensor, including measured parameter, measurement principle, measuring range, resolution, accuracy, repeatability, and response time (T90)
- Statement of the governing USEPA, ASTM, ISO, or Standard Methods procedure for each parameter, and, for compliance instruments, documentation that the analyzer is approved for online compliance monitoring under that method
- Sensor data: wetted materials, body and cable rating (IP/NEMA), pressure and temperature limits, flow requirements, and fouling/cleaning provisions
- Sample conditioning provisions: sample tap location and pressure, strainer/filter, constant-head or flow-control device, sample pump where required, flow cell, sample-panel arrangement drawing, and sample-line material and size
- Reagent data for wet-chemistry analyzers: reagent identity and Safety Data Sheets, consumption rate, container size, replacement interval, and shelf life
- Calibration provisions: calibration method (buffer, standard solution, span gas, or factory-characterized), the reference standards/buffers required, calibration frequency, and the grab-sample verification procedure for compliance instruments
- Automatic temperature compensation method and the reference temperature
- Output and communication data: analog output (4-20 mA / HART), fault-signal levels per NAMUR NE43, digital protocol where provided, and the list of measured values, diagnostics, and alarms available
- Power requirements, enclosure rating, and area-classification listing where the analyzer is in a classified location
- Instrument loop diagrams and the instrument index/tag list per ANSI/ISA-5.1, and the point list for integration with Control Systems Integration
- Mounting and installation details, including washdown and maintenance access
☐ Product data with range, accuracy, and response time
☐ Governing method and compliance-monitoring approval
☐ Sensor wetted materials, ratings, and cleaning provisions
☐ Sample conditioning / sample-panel arrangement
☐ Reagent data and Safety Data Sheets (wet-chemistry analyzers)
☐ Calibration method, standards/buffers, and frequency
☐ Temperature compensation method
☐ Output, NAMUR NE43 fault levels, and digital protocol
☐ Power, enclosure rating, and area classification
☐ Loop diagrams and ISA-5.1 instrument index / point list
☐ Mounting and washdown/maintenance access details
3.1.2Fabrication and procurement shall not proceed until action submittals have been reviewed and returned.
3.2 Closeout Submittals
3.2.1At substantial completion, the Contractor shall provide the following before the analyzers are accepted.
- Operation and maintenance manuals for each analyzer, organized with a table of contents, including manufacturer's installation, calibration, operation, and maintenance instructions
- As-calibrated record for each analyzer: initial calibration values, the reference standards/buffers used, and, for compliance instruments, the initial grab-sample verification result
- Factory calibration certificates traceable to recognized reference standards where furnished
- Reagent inventory and the documented replacement interval and consumption rate for each wet-chemistry analyzer
- Recommended calibration and maintenance schedule for each analyzer (calibration frequency, sensor cleaning, electrolyte/membrane or reagent replacement, consumable life)
- Loop checkout and signal-verification records confirming the output reads correctly at the control system and that the NAMUR NE43 fault levels report correctly
- Spare parts inventory list with manufacturer part numbers
- Warranty documentation, including any separate sensor or membrane warranty
☐ Operation and maintenance manuals
☐ As-calibrated record and reference standards used
☐ Factory calibration certificates (where furnished)
☐ Reagent inventory and replacement interval
☐ Calibration and maintenance schedule
☐ Loop checkout and signal-verification records
☐ Spare parts inventory list with part numbers
☐ Warranty documentation
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1Analyzers shall be the products of a manufacturer with a minimum of ten years of continuous experience producing online analytical instrumentation of the type specified for water, wastewater, or industrial process service.
4.1.2Replacement sensors, reagents, consumables, and factory service support for the analyzer model line shall be available for a minimum of ten years from the date of manufacture.
4.1.3The manufacturer shall maintain an ISO 9001 certified quality management system.
4.2 Method Compliance
4.2.1Each analyzer shall measure its parameter in accordance with the governing USEPA, ASTM, ISO, or Standard Methods procedure identified for that parameter in this standard.
4.2.2Where an analyzer serves a drinking-water or discharge compliance-monitoring function, it shall be a type approved for online compliance monitoring under the applicable USEPA method, and the approval shall be documented in the submittal.
NOTE Online turbidimeters used for drinking-water compliance reporting shall meet the design and performance requirements of USEPA Method 180.1, including the white-light (tungsten) source design that the method specifies for compliance instruments. (4.2.3)
NOTE Online chlorine analyzers used for drinking-water compliance reporting shall comply with USEPA Method 334.0, which permits any online analyzer technology (amperometric or DPD-colorimetric) provided the analyzer is verified against an approved grab-sample reference method. (4.2.4)
NOTE A turbidimeter that meets ISO 7027 (near-infrared LED source) but not USEPA Method 180.1 is acceptable for process control and for non-compliance monitoring, but is not acceptable as the reportable compliance instrument for a USEPA-regulated drinking-water filtration plant; the white-light and near-infrared methods are not interchangeable for compliance and read differently on the same sample. (4.2.5)
4.3 Factory Calibration and Verification
4.3.1Each analyzer shall be factory-calibrated and tested before shipment, and the factory calibration shall be traceable to recognized reference standards.
4.3.2Sensors that are characterized at the factory (pre-calibrated, data-coded sensors) shall be furnished with the calibration data recorded so the value is restored when the sensor is installed or replaced.
NOTE Pre-characterized digital sensors that store their calibration in the sensor head let a fouled or aged sensor be swapped for a freshly calibrated one in the field in minutes, with calibration performed offline in a clean shop environment rather than in the process; this is the single largest maintenance-labor saving available in modern analytical instrumentation. (4.3.3)
5 Environmental and Service Conditions
5.1 Installation Environment
NOTE Analyzers and their sensors shall be selected and rated for the conditions at the installation point, including the process temperature and pressure, the ambient temperature and humidity, washdown exposure, and any corrosive or classified-area conditions. (5.1.1)
Indoor process area — climate-controlled or partially controlled
Indoor wet/washdown area — treatment gallery or pump room
Outdoor — sheltered (canopy or instrument enclosure)
Outdoor — fully exposed, weatherproof rated
Submerged/basin-mounted — sensor in open tank or channel
Classified (hazardous) location — see area classification
5.1.2Analyzers and sensors installed in wet or washdown areas shall be rated NEMA 4X (or IP66) or better.
5.1.3Outdoor and basin-mounted analyzers shall be rated for the project climate, including freeze protection of any sample line, flow cell, or reagent that can freeze, and shielding of optical and electronic components from direct sun and weather.
5.1.4Where the analyzer is installed in a classified (hazardous) location, the analyzer, sensor, and wiring shall carry the area-classification listing required by NFPA 70 for the location.
5.2 Area Classification
Unclassified (general purpose)
Class I, Division 2
Class I, Division 1
Class I, Zone 1
Class I, Zone 2
NOTE Digester gas, chemical storage, and certain wastewater process areas are commonly classified locations; an analyzer installed there without the correct listing is a code violation and a safety hazard. (5.2.2)
6 Measured Parameters
6.1 Parameter Selection
NOTE Each measured parameter is a distinct analyzer with its own sensor technology, calibration regime, and maintenance burden; selecting parameters and counts is a process-design decision driven by the treatment process, the regulatory monitoring obligations, and the control strategy. (6.1.2)
☐ pH
☐ ORP (oxidation-reduction potential)
☐ Turbidity
☐ Free chlorine residual
☐ Total chlorine residual
☐ Chloramine / monochloramine
☐ Dissolved oxygen (DO)
☐ Conductivity
☐ Ammonia (ammonium / total ammonia nitrogen)
☐ Nitrate
☐ Ozone residual
☐ Total organic carbon (TOC) / UV-254
☐ Total suspended solids (TSS) / sludge blanket
☐ Streaming current (coagulation control)
6.2 pH
6.2.1pH shall be measured electrometrically with a glass measuring electrode and a reference electrode in accordance with ASTM D1293 (Test Method B for continuous measurement) and ASTM D6569 for online measurement.
6.2.2The pH sensor shall include automatic temperature compensation referenced to 25°C.
NOTE pH is temperature-dependent at the electrode; without automatic temperature compensation a reading drifts with process temperature and is not reportable. (6.2.3)
NOTE The combination glass/reference pH sensor is the standard for nearly all water and wastewater service because it is unaffected by color, turbidity, and most oxidants and reductants; the chief failure modes are reference-junction fouling and glass-bulb aging, which set the cleaning and replacement interval. (6.2.4)
○ Combination glass / reference electrode — analog
○ Combination glass / reference electrode — digital (pre-characterized sensor head)
○ Differential (three-electrode) — high-fouling / heavy industrial service
014
2468101214
Default: 14 pH
6.2.5pH sensors shall be calibrated against certified buffer solutions at a minimum of two buffer points that bracket the process operating range (typically pH 4, 7, and 10 buffers).
6.3 ORP
6.3.1Oxidation-reduction potential (ORP) shall be measured with a platinum (or gold) measuring electrode against a reference electrode in accordance with ASTM D1498, reported in millivolts.
NOTE ORP is used to infer disinfection capacity, dechlorination endpoint, and the redox state of a process (for example, the oxidation step in cyanide or chrome treatment), not to measure a specific chemical concentration. (6.3.2)
6.3.3ORP sensors shall be calibrated against a certified ORP standard solution (for example, a quinhydrone or ZoBell reference solution).
-15001500
-1500-1000-50050010001500
Default: 1500 mV
6.4 Turbidity
6.4.1Turbidity shall be measured by nephelometry — detection of light scattered at 90° by suspended particles — and reported in NTU (nephelometric turbidity units) or, for ISO 7027 instruments, in FNU/NTU as the method defines.
NOTE The turbidimeter measurement method shall match the use: USEPA Method 180.1 (white-light tungsten source) where the instrument is a drinking-water compliance instrument, or ISO 7027 (near-infrared LED source) for process control and where color interference must be minimized. (6.4.2)
○ USEPA Method 180.1 — white-light (tungsten) source — drinking-water compliance
○ ISO 7027 — near-infrared LED source — process control / low-color interference
0 to 10 NTU — filtered / finished water (low-range, compliance)
0 to 100 NTU — settled / process water
0 to 1000 NTU — raw / source water
0 to 4000 NTU — high-solids / raw water
NOTE Filter-effluent and combined-filter-effluent turbidimeters at a surface-water treatment plant are the principal compliance instruments for the filtration process and shall be the low-range compliance type. (6.4.3)
6.4.4Turbidimeters shall be calibrated against the manufacturer's primary turbidity standard (formazin or an approved equivalent) at the intervals required by the governing method.
NOTE Bubbles in the sample are the most common cause of a falsely high turbidity reading; the sample conditioning shall include a bubble trap or a flow-through cell designed to deaerate the sample. (6.4.5)
6.5 Chlorine Residual
6.5.1Chlorine residual shall be measured online by an amperometric or DPD-colorimetric analyzer in accordance with USEPA Method 334.0 where the analyzer serves a drinking-water compliance-monitoring function, and otherwise in accordance with Standard Methods 4500-Cl for the equivalent process measurement.
NOTE The analyzer shall measure the chlorine species required by the process — free chlorine, total chlorine, or both — and, where chloramination is used, the monochloramine or total chlorine appropriate to the disinfectant. (6.5.2)
Free chlorine residual
Total chlorine residual
Free and total chlorine (combined determines chloramines)
Monochloramine (chloramination)
○ Amperometric — reagent-free or low-reagent membrane sensor
○ DPD colorimetric — reagent-based (matches lab DPD reference)
NOTE The amperometric reagent-free sensor avoids the reagent inventory and reagent-handling burden of the DPD method but requires a controlled, constant sample flow and pH within the sensor's compensation range; the DPD method directly matches the laboratory grab-sample reference but consumes reagent continuously and generates a reagent waste stream. (6.5.3)
NOTE A compliance chlorine analyzer is valid only within USEPA Method 334.0's stated working range (approximately 0.2 to 4 mg/L); readings outside that range shall be confirmed by an approved grab-sample method for compliance reporting. (6.5.4)
6.5.5The online chlorine analyzer shall be verified against an approved grab-sample reference method (DPD colorimetric or amperometric titration), and shall agree with the grab sample within ±0.1 mg/L or ±15%, whichever is greater, per USEPA Method 334.0.
6.6 Dissolved Oxygen
6.6.1Dissolved oxygen shall be measured by an optical (luminescence-based) sensor in accordance with ASTM D888 Method C and ISO 17289, or by an electrochemical (membrane/galvanic or polarographic) sensor in accordance with ASTM D888 Method B.
○ Optical (luminescent / LDO) — no membrane or electrolyte, low maintenance
○ Electrochemical (membrane galvanic or polarographic)
020
5101520
Default: 20 mg/L
NOTE The optical DO sensor is the default for activated-sludge aeration-basin service because it has no membrane to replace and no electrolyte to refill, holds calibration far longer than an electrochemical cell, and does not consume oxygen at the sensor face (so it does not require sample flow across the membrane). (6.6.2)
6.6.3DO sensors shall include automatic temperature compensation and shall be calibrated to water-saturated air (100% saturation) or against a zero-oxygen standard as the method requires.
NOTE Aeration-basin DO is the principal control input for blower and aeration control; an inaccurate DO reading drives either energy waste (over-aeration) or a process upset (under-aeration), so the DO sensor calibration directly governs the largest energy cost at most wastewater plants. (6.6.4)
6.7 Conductivity
6.7.1Conductivity (specific conductance) shall be measured in accordance with ASTM D1125 and Standard Methods 2510, reported in µS/cm or mS/cm and temperature-compensated to 25°C.
○ Contacting (two- or four-electrode) — low to moderate conductivity
○ Toroidal (inductive) — high conductivity, fouling, or corrosive service
0 to 200 µS/cm — high-purity / RO permeate
0 to 2000 µS/cm — drinking / process water
0 to 20 mS/cm — wastewater / brackish
0 to 200 mS/cm — brine / high-salinity
NOTE Toroidal (inductive) sensors have no exposed electrodes to foul or polarize and are preferred for wastewater, high-conductivity, and fouling service; contacting sensors offer better resolution at low conductivity and are preferred for high-purity-water service. (6.7.2)
6.7.3Conductivity sensors shall be calibrated against a certified conductivity standard solution appropriate to the measuring range, and the sensor cell constant shall be entered or verified at calibration.
6.8 Additional Process Analyzers
NOTE Where indicated, the following additional online analyzers shall be provided and shall measure in accordance with the governing method noted. (6.8.1)
NOTE Ammonia (total ammonia nitrogen / ammonium) shall be measured by ion-selective electrode or colorimetric analyzer per Standard Methods 4500-NH3, commonly for aeration and nitrification control and for effluent monitoring. (6.8.2)
NOTE Nitrate shall be measured by ion-selective electrode or by ultraviolet absorption per Standard Methods 4500-NO3, commonly for denitrification control and effluent monitoring. (6.8.3)
NOTE Ozone residual shall be measured by an amperometric or colorimetric analyzer per Standard Methods 4500-O3 where ozone is used for disinfection or oxidation. (6.8.4)
NOTE Total organic carbon (TOC), and the surrogate UV absorbance at 254 nm (UV-254), shall be measured per USEPA Method 415.3 for source-water and disinfection-byproduct-precursor monitoring and for coagulation optimization. (6.8.5)
NOTE Suspended solids and sludge-blanket level shall be measured by optical (light-scatter or absorption) sensors for clarifier, thickener, and mixed-liquor (MLSS) monitoring. (6.8.6)
NOTE Streaming current shall be measured by a streaming-current monitor for automatic coagulant-dose (coagulation) control; it reads net particle charge, not a concentration, and is paired with downstream turbidity and, where used, UV-254. (6.8.7)
☐ Ammonia — ISE or colorimetric (SM 4500-NH3)
☐ Nitrate — ISE or UV (SM 4500-NO3)
☐ Ozone residual — amperometric or colorimetric (SM 4500-O3)
☐ TOC / UV-254 (USEPA 415.3)
☐ TSS / MLSS / sludge blanket — optical
☐ Streaming current — coagulation control
7 Sample Conditioning and Mounting
7.1 Mounting Method
NOTE The mounting method shall suit the parameter, the sensor technology, and the access available. (7.1.1)
NOTE In-situ (insertion or submersible) mounting places the sensor directly in the process pipe, channel, or basin; it has the fastest response and no sample-line lag, but the sensor is exposed to the full process fouling and the sensor must be removable for service without a process shutdown. (7.1.2)
NOTE Flow-through mounting feeds a conditioned sample to a sensor in a flow cell on a sample panel; it isolates the sensor from process pressure and debris, allows bubble removal and flow control, and keeps the sensor at a convenient service height, at the cost of sample-line lag and the maintenance of the sample system itself. (7.1.3)
○ In-situ insertion — sensor in process pipe with retractable/ball-valve fitting
○ In-situ submersible — sensor on a float or rail in an open basin/channel
○ Flow-through — sensor in a flow cell fed from a sample tap (sample panel)
7.1.4Insertion sensors in pressurized pipe shall be installed in a retractable fitting or behind an isolation/ball valve so the sensor can be withdrawn for cleaning and calibration without depressurizing or shutting down the process.
7.2 Sample System
7.2.1Flow-through analyzers shall be furnished with a sample-conditioning system that delivers a clean, bubble-free, flow-controlled, and pressure-controlled sample to the sensor.
☐ Isolation valve at the sample tap
☐ Strainer or self-cleaning filter
☐ Pressure-reducing or constant-head device
☐ Sample flow indicator and flow-control valve
☐ Bubble trap / deaeration
☐ Low-sample-flow alarm switch
☐ Sample pump (where tap pressure is insufficient)
☐ Calibration / grab-sample valve at the flow cell
7.2.2A constant-head device or pressure regulator shall be provided where the sensor requires a steady flow or pressure; amperometric chlorine sensors in particular read in error if the sample flow varies.
NOTE A low-sample-flow alarm shall be provided so the control system can flag a reading as invalid when sample flow is lost; a sensor reading a stagnant or empty flow cell will report a plausible but meaningless value. (7.2.3)
7.2.4The sample lag time (the transport delay from the tap to the sensor) shall be minimized and shall be documented, because lag delays the analyzer's response to a process change and degrades any control loop the analyzer feeds.
7.3 Sample Panel
7.3.1Where multiple flow-through analyzers share a location, they shall be arranged on a common sample panel with the sensors, flow cells, sample valves, flow indicators, and analyzers mounted for operation and service from the front.
7.3.2Sample panels shall be fabricated from corrosion-resistant materials suitable for the chemicals and washdown of the installation, and sample tubing shall be of a material compatible with the sample chemistry and any disinfectant residual.
7.4 Reagent Handling
7.4.1Wet-chemistry analyzers shall be furnished with reagent containers sized for a practical replacement interval, and the reagent consumption rate, container size, and replacement interval shall be documented.
Reagent-free / membrane sensor — no reagent
30 days
60 days
90 days
7.4.2Reagent waste and spent-reagent drainage shall be routed to an appropriate drain or collection point, and reagents shall be handled per their Safety Data Sheets.
NOTE Reagent inventory is a recurring operating cost and a maintenance task; where a reagent-free sensor (such as an amperometric chlorine or optical DO sensor) meets the measurement requirement, it should be preferred to reduce operator burden. (7.4.3)
8 Calibration and Temperature Compensation
8.1 Temperature Compensation
8.1.1Every analyzer whose reading is temperature-dependent — pH, conductivity, dissolved oxygen, amperometric chlorine, and others — shall include automatic temperature compensation, with the compensation referenced to 25°C unless the governing method specifies otherwise.
NOTE An uncompensated temperature-dependent reading is not a valid measurement; for conductivity, a 1°C change shifts the reading on the order of 2%, so temperature compensation is not optional on any reportable conductivity or pH instrument. (8.1.2)
8.2 Calibration Frequency and Standards
8.2.1Each analyzer shall be calibrated at startup and recalibrated at the manufacturer's recommended frequency for the parameter and service, using the certified reference standards, buffers, or grab-sample reference method appropriate to the parameter.
Certified buffer solutions (pH)
Certified standard solution (ORP, conductivity)
Primary turbidity standard (formazin or approved equivalent)
Air-saturation / zero-oxygen standard (dissolved oxygen)
Grab-sample verification against approved reference method (chlorine, compliance instruments)
Factory-characterized / data-coded sensor (no field standard)
Weekly
Monthly
Quarterly
Per regulatory monitoring requirement
Per manufacturer recommendation
8.2.2For compliance instruments, the calibration and verification frequency shall meet the minimum required by the applicable regulation, which may be more frequent than the manufacturer's recommendation.
8.2.3Calibration of a compliance analyzer shall be documented with the reference value, the analyzer value, and the date, and the record shall be retained for the period the regulation requires.
NOTE Over-frequent calibration of a stable sensor introduces more error and drift than it removes, while under-frequent calibration lets a fouled sensor drift out of compliance unnoticed; the frequency should be set from the actual observed drift between verifications, not chosen conservatively by default. (8.2.4)
9 Signal Output and Integration
9.1 Analog Output
9.1.1Each analyzer shall provide an isolated 4-20 mA analog output for each measured value, scaled to the measuring range, in accordance with ANSI/ISA-50.00.01.
NOTE The analog output shall implement NAMUR NE43 fault signaling, driving the loop to 3.6 mA or below (or 21 mA or above) on a detected analyzer fault so the control system distinguishes a fault from a valid in-range reading. (9.1.2)
○ Downscale fault (≤ 3.6 mA) — fault reads as low (standard)
○ Upscale fault (≥ 21 mA) — fault reads as high
NOTE A reading that is merely out of range shall be distinguishable from an instrument fault; a turbidimeter reading 0.00 NTU because its lamp has failed must not be mistaken for genuinely clean water. (9.1.3)
9.2 Digital Communication
4-20 mA with HART
4-20 mA only (no digital)
Modbus RTU (RS-485)
Modbus TCP/IP (Ethernet)
EtherNet/IP
PROFIBUS / PROFINET
9.2.2The analyzer shall make available, in addition to the primary measured value, the diagnostic and status information (sensor health, calibration status, fault, and where applicable the compensating temperature and sample flow) needed for the control system to validate the reading.
9.3 Tagging and Loop Identification
10 Installation
10.1 Sensor Location
10.1.2Sensors shall be located in a representative, well-mixed portion of the process stream, away from chemical injection points by enough distance for complete mixing, and away from dead legs, air pockets, and stratified flow that would give an unrepresentative reading.
NOTE A chlorine or pH sensor placed too close to the chemical feed point reads the unmixed chemical, not the process; the sample point shall allow complete mixing before measurement. (10.1.3)
10.2 Access and Washdown
☐ Sensor removable for cleaning/calibration without process shutdown
☐ Service clearance for sensor withdrawal and flow-cell access
☐ Washdown-rated enclosure and fittings
☐ Local display/keypad accessible at standing height
☐ Eyewash/safety station near reagent handling (where required)
10.2.1Each analyzer and sensor shall be installed so it can be cleaned, calibrated, and serviced without a process shutdown and without removing adjacent equipment.
10.2.2Analyzers and sensors in washdown areas shall have their enclosures, cable entries, and fittings oriented and sealed to shed washdown water, and local displays shall be readable and keypads reachable from a normal standing position.
10.3 Power and Wiring
10.3.1Analyzer power, grounding, and signal wiring shall be installed per NFPA 70 and the project electrical standards, with signal wiring run separately from power wiring and shielded where the manufacturer requires, to protect the low-level analytical signal from electrical noise.
NOTE Sensors with low-level or high-impedance signals (notably pH and ORP) shall use the manufacturer's specified cable and run length limits, because the high-impedance pH signal is especially susceptible to noise and moisture in the connection. (10.3.2)
11 Testing and Commissioning
11.1 Loop Checkout
11.1.1Each analyzer signal shall be loop-checked from the sensor through the analyzer output to the control system, verifying that the value reads correctly at the Scada And Hmi Systems and that the NAMUR NE43 fault levels report correctly. 11.2 Calibration and Verification
11.2.1Each analyzer shall be calibrated at startup against its reference standard, buffer, or grab-sample reference method, and the as-calibrated values shall be recorded.
11.2.2Each compliance analyzer shall be verified against the approved grab-sample reference method at startup, and the verification result shall meet the agreement criterion of the governing method (for online chlorine, ±0.1 mg/L or ±15% per USEPA Method 334.0).
☐ Loop checkout record (sensor to SCADA)
☐ NAMUR NE43 fault-level verification
☐ As-calibrated values and reference standards used
☐ Grab-sample verification for compliance instruments
☐ Sample-flow and low-flow-alarm verification
☐ Temperature-compensation verification
11.2.3Sample flow, the low-sample-flow alarm, and temperature compensation shall each be verified to function before the analyzer is accepted.
11.3 Demonstration
11.3.1The Contractor shall demonstrate to the Owner the routine calibration, sensor cleaning, reagent replacement (where applicable), and consumable replacement for each analyzer type, and shall provide hands-on training to the Owner's operations staff.
12 Delivery, Storage, and Handling
12.1Analyzers, sensors, reagents, and reference standards shall be delivered in the manufacturer's packaging and protected from freezing, heat, and physical damage.
12.2pH, ORP, and reference sensors shall be stored with their bulbs and junctions kept wet in the manufacturer's storage solution; a sensor allowed to dry out may be permanently degraded.
12.3Reagents and reference standards shall be stored within their labeled temperature range and shall not be installed past their shelf-life or expiration date.
12.4Optical sensors shall be protected from scratches and contamination of the optical window until installed.
13 Warranty
13.1 Warranty Terms
13.1.1The manufacturer shall warrant each analyzer against defects in materials and workmanship for a minimum of one year from substantial completion.
13.1.2Sensors and measuring cells shall carry the manufacturer's standard sensor warranty, recognizing that pH, chlorine, and DO sensors are consumable items with a finite service life.
13.1.3Consumable items — buffers, reagents, electrolyte, membranes, and reference standards — are not warranted as defects when consumed in normal service.
14 Spare Parts
14.1 Spare Parts Package
14.1.1The Contractor shall furnish the manufacturer's recommended spare parts and consumables for the first year of operation.
- One spare sensor of each type provided (pH, ORP, chlorine, DO, conductivity, and others as applicable)
- Membranes, electrolyte, and O-rings for each electrochemical sensor
- One replacement reagent set for each wet-chemistry analyzer
- Calibration buffers and reference standards for each parameter
- Recommended electronic spares (output module or analyzer board) where identified by the manufacturer
☐ One spare sensor of each type
☐ Membranes, electrolyte, and O-rings (electrochemical sensors)
☐ One replacement reagent set (wet-chemistry analyzers)
☐ Calibration buffers and reference standards
☐ Recommended electronic spares
14.1.2The spare-parts list with manufacturer part numbers shall be included in the closeout documentation.