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Chemtrac, Inc./ Products/ Streaming Current/ Streaming Current Sensor
DuraTrac-4
HydroACT-600
HydroACT 600 Screenshot
Installation Diagram
HA600-Sensor-Status-Screenshot
DuraTrac-4
HydroACT-600
HydroACT 600 Screenshot
Installation Diagram
HA600-Sensor-Status-Screenshot

Streaming Current Sensor

DuraTrac 4

The HydroACT 600 with DuraTrac 4 Streaming Current Sensor (a.k.a. Streaming Current Monitor or Streaming Current Detector) provides a very robust sensor design with advanced capabilities for online charge measurement and coagulation control.  The unique features of the DuraTrac 4 sensor include: a simple method for calibrating the Streaming Current reading, optional conductivity compensation, user serviceable probe, extended service life motor, and a diagnostic measurement of signal health. 

With expansive I/O, state of the art chemical feed control logic, and the optional ability to monitor additional parameters key to coagulation like pH, UV254, and NTU, Chemtrac's HydroACT family of multi-parameter analyzers provides an extremely versatile system for optimizing coagulant or polymer dosing.

The HydroACT 600 with DuraTrac 4 Streaming Current Sensor provides an extremely versatile system for optimizing coagulant or polymer dosing. With expansive I/O, state of the art chemical feed control logic, and the ability to monitor additional parameters key to coagulation (e.g. pH, UV254, NTU), the HydroACT 600 offers a comprehensive and scalable approach for tackling virtually any water treatment scenario. An optional web browser based user interface gives the user remote access to everything they need to reliably control multiple feed systems (coagulant, flocculant, chlorine, acid, caustic, etc). Intelligent diagnostics, advanced alarm features, and optional email/text alerts all work together to notify the user when service is required or when process conditions having changed sufficiently to warrant attention. Contact Chemtrac to discuss your application and let us provide a solution that meets your requirements.

Standard Features
  • Highest measurement repeatability, minimum impact from conductivity swings
  • Advanced diagnostics with Signal Health Alert
  • Quick-replacement probe with user-replaceable parts
  • Color display with graphical trending capability
  • Data logging with micro SD card slot for data download
  • Automatic Gain and Zero Adjust features
  • 2 year warranty
Optional Features
  • pH compensation setting for Streaming Current signal
  • Accepts up to 5 additional sensor inputs (e.g. UV254, TSS/NTU, pH, Chlorine, Conductivity)
  • Up to 6 chemical feed control outputs with Overfeed Protection and Flow Pacing capability
  • Remote access via web server over LAN or GSM modem with email or text alerts
  • Automatic Flush, and Sensor Clean
  • Modbus, PROFIBUS, or HART communications
  • Touchscreen (with larger display)
Benefits
  • Improved measurement capabilities significantly reduces impact of conductivity and pH swings on the Streaming Current reading 
  • Capability of incorporating multiple measurements that are key to coagulation, such as pH, TSS/NTU, and UV254
  • Signal Health diagnostic feature provides higher degree of confidence in both measurement reliability and automated coagulant dosing
  • Rugged design and user-serviceable parts greatly reduce cost of ownership

DuraTrac 4 Streaming Current Sensor

Range

-1000 to +1000

Signal Gain

User-adjustable, 1 to 600x

Zero Offset

User-adjustable

Sample Flow Rate

1 - 40 Liters per minute

Gain & Zero Offset

User-adjustable, Manual or Automatic

Repeatability (Conductivity Range)*

Better than 2% from (10 to 250 μS)

Better than 3% from (250 to 500 μS)

Better than 5% from (500 to 1000 μS)

Max Pressure

30 psi

Sample Cell Type

External receiver, high flow

 

Probe Type

Quick-replacement cartridge with replaceable sleeve

Piston Type

Quick-replacement

Sample Connections

1” FNPT

Materials Contacting Sample

Delrin, viton, stainless steel

Wiring Connections

1 ea. shielded, 4 conductor, 22 AWG

Self Diagnostics

Motor - RPM, Signal Health

Power Requirements

110 VAC, 1 A, 60 Hz 220 VAC, 1 A, 50 Hz (optional)

Enclosure

NEMA 4X, fiberglass reinforced

Operating Temperature

34° - 120° F (1° - 49° C)

Dimensions

11.2” W x 9.2” H x 6.3” D
(285 mm W x 234 mm H x 161 mm D)

Weight

10 lbs (4.5 kg)

HydroACT 600 Analyzer

Sensor Options

SCM, UV254 organics, TSS/NTU, Free Cl,“Zero” Free Cl, Total Cl, Cl Dioxide, Ozone, pH with Temperature, ORP, DO, Conductivity, Chlorite, Biofilm, Particle Counter

Measurement Parameters

Up to 6 (some sensors may count as multiple measurement parameters; check with factory)

4-20mA Outputs

Up to 6 (750 ohm load); PID option will utilize 1 output

Relays

Up to 8 (250 VAC, 8A / 30 VDC, 8A)

Digital Inputs

Up to 4 (e.g. low flow switch, process run/stop)

Chemical Feed Control

Up to 6 loops, control options include: PID, flow pacing, timer

Display Options

1/4 VGA color display; or 5.7” touchscreen

Comms Options

Modbus (RTU, TCP), PROFIBUS, or HART

Datalogging

Minimum 4000 data points per channel without micro SD card (datalogging can be expanded with micro SD card)

Graphing

Last 400 logged data points

Event Logging

4000 events

micro SD Slot

1 (for data download & memory expansion)

Expansion Slots

4 (for digital comms, modem)

Power Options

100-240 VAC, or 12 VDC

Enclosure

Nema 4X/IP65, ABS body, Polycarbonate lid

Dimensions

9.0” W x 9.3” H x 5.3” D (230 mm W x 237 mm H x 135 mm D)

Weight

4.4 lbs (2 kg)

 *Applicable as of July 1, 2014.  Some competitor's specifications for repeatability are based on there being a stable conductivity.  For most of these, even small changes in conductivity (e.g. 150 to 200 uS) can cause the streaming current reading to change by >10%!

DuraTrac 3 & DuraTrac 4 / Operation ManualsVersionLanguagesSizeDate
DuraTrac 3 Operation Manual
DuraTrac 3 Operation Manual
1.8 MiB02/11/2014
DuraTrac 4 Operation Manual
DuraTrac 4 Operation Manual
1.7 MiB09/05/2014
DuraTrac 3 & DuraTrac 4 / DatasheetsVersionLanguagesSizeDate
HydroACT 600 & DuraTrac 3 Datasheet
HydroACT 600 & DuraTrac 3 Datasheet
653.8 KiB10/16/2013
HydroACT 600 & DuraTrac 4 Datasheet
HydroACT 600 & DuraTrac 4 Datasheet
711.3 KiB09/05/2014
Streaming Current Monitors (SCM) are used to detect the net charge of soluble (e.g. organics) and insoluble (e.g. colloidal particulate) species in water. This is an extremely useful measurement because the net charge of colloidal and soluble contaminants in water will determine whether those contaminants are stabilized in suspension, or destabilized enough with the use of cationic coagulants to allow for more efficient removal via settling or filtration. A Streaming Current Monitor will respond to changes in the feed water turbidity as well as organics. Natural organic matter (NOM) will generally produce a significant response on a Streaming Current Monitor due to its high anionic charge. The ability to measure charge responses associated with both organic and particulate contaminants is what allows Streaming Current Monitors to reliably optimize coagulant dosage.
Streaming current is a very small electric current which is developed when water containing electrolytes is rapidly passed across a surface, such as what occurs when water is forced through a thin capillary. An identifying feature of a Streaming Current or Streaming Potential measurement device, like those used in water treatment, is a reciprocating piston that travels inside of a probe. The probe itself is composed of a dead end bore with electrodes positioned at either end. The vertical up and down movement of the piston causes water to be pulled into and then discharged from the probe’s bore. The clearance between the piston and probe walls is usually very small (e.g. 0.010 in) and this serves to create the “shearing zone” that gives rise to the streaming current signal.

This Streaming Current arises due to these high shear forces acting upon a surface’s electrical double layer (EDL), which can be thought of as an atmosphere of charged atoms (ions) that appear on a wetted surface, such as the surface of a colloid, or in a larger context the surface of Streaming Current Detector’s piston. This atmosphere of charge is composed of a stern and diffuse layer (hence the term “double layer”) of positively and negatively charged ions. The shearing action of the water causes the separation of ions from the diffuse layer which in turn produces the “streaming current”. This signal is then amplified and processed by the SCM’s electronics where it is then displayed as the streaming current reading.
Zeta Potential (ZP) is the electrokinetic potential that exists at a colloids surface and is expressed in mV’s. Measurements of Streaming Current are not a direct measurement of Zeta Potential, although it is fair to say they are closely related for reasons described in the previous FAQ “How is the Streaming Current signal produced”. While it is useful to think of Streaming Current as a pseudo Zeta Potential measurement, it should always be made clear that any correlation between the two is not constant and trying to keep an online Streaming Current Meter reading calibrated to a laboratory determination of Zeta Potential is a very tedious task for most water plants and therefore rarely done.

It is more commonly accepted the relative measurement of electrokinetic potential provided by Streaming Current Meters is very useful as a process monitoring and control tool without needing to calibrate it to a ZP value, as long as the user makes occasional determinations of an optimum Streaming Current setpoint reading using jar testing or other methods (see FAQ “How do I determine my Streaming Current setpoint?).
Instruments used to measure Streaming Current go by many various names depending on manufacturer: streaming current monitor, streaming current analyzer, streaming current detector, streaming current meter, streaming potential analyzer, streaming potential detector, particle charge detector, particle charge analyzer, etc..

Some of these instruments will measure the electrical voltage potential (properly referred to as streaming potential) that results from the streaming current affect, while others measure the actual current itself. An instrument that is called Streaming Current might actually be technically measuring Streaming Potential.
It is an interesting fact that you will not see much agreement between manufacturers in how the Streaming Current reading is displayed. Some show the reading as -10.00 to +10.00, while another goes from -100.0 to +100.0, and while another still goes from -1000 to +1000. Part of the reason for this is because Streaming Current has long been accepted as a relative and unit-less number. So, decimal point or no decimal point is just personal taste of that manufacturer and not any kind of indication of measurement accuracy or sensitivity.

Chemtrac has adopted a range of -1000 to +1000 and uses the term “Streaming Current Value” (SCV) and sometimes “Streaming Current Unit” (SCU) for the units of measurement.
Online Streaming Current Meters (SCM) are used in various industries and applications. A very common use of Streaming Current Meters is for optimizing coagulant dosage in water treatment. The SCM allows the user to more accurately control the addition rate of the coagulant to maintain a setpoint charge reading that correlates to optimum treatment results. Other common applications for Streaming Current Meters include polymer control for wastewater treatment and wet end charge monitoring in the pulp and paper industry.
For many water treatment applications, if installation is done correctly and as advised by the manufacturer, then the odds are that a Streaming Current Detector (SCD) will provide a useful benefit and in many cases can be used to automate coagulant dosing. However, not all applications are a good fit for this technology. Water chemistry and the exact type of coagulant being used play a huge role in determining whether a Streaming Current Detector is a good fit. In some cases, the chemistry and coagulant selection are not the problem. The problem is sometimes to do with process design. Mainly in how and where the coagulant is being injected and mixed, and where a sample can be taken. In many of these cases, injection points and samples points can be moved around to better accommodate an SCD.

So how do you know if a Streaming Current Detector is the right choice for your application? Before making any decisions, we highly recommends a consultation with one of our application experts. Chemtrac has over 25 years of experience helping thousands of water treatment plants determine whether a Streaming Current Detector is the right tool for them. If we can’t make a confident determination over the phone, we will ask for samples to be sent to our lab for testing and/or come onsite to perform an onsite evaluation.
To help us determine whether a Streaming Current Analyzer is right for your application, please gather the following information before contacting our application specialist:

1) Type of coagulant and/or polymer being used (e.g. alum, ferric, PACl, ACH), as well as a listing of all other additives fed upstream of where the SCM sample is to be located. Provide expected min, max, and average dosages of each chemical. If feeding PACl, please determine the products basicity. For any coagulant aids or flocculants, be sure to determine whether these are cationic or anionic.

2) The min, max, and average values for the following water chemistry variables: pH, alkalinity, temperature, and conductivity.

3) The min, max, and average for these raw water quality and process variables: NTU (or TSS), organics (TOC), process flow rate.

4) Exact location where coagulant is being injected relative to other additives and mixing devices. A simple hand drawn diagram is very helpful.

5) Location where the SCM sample point will be located, and how far downstream in seconds/minutes that is expected to be from coagulant injection point. This is very important to determine somewhat accurately!

6) Location where the sensor will be mounted relative to the sample point. Its best to not use long sample lines if they can be avoided.

7) For water treatment, provide a listing of the plants water source(s). It is very important to note if the plant will sometimes switch source waters.

8) For wastewater, list the type of industry (e.g. food, petrochemical, paper, etc). Wastewater will require many more questions to be answered during the phone consultation.
This is a very important question and something that is often not well understood. The Streaming Current Analyzer should be installed as close to coagulant injection as possible. When it comes to charge measurements, seconds matter! In some situations, the cationic charge that appears with the introduction of a coagulant is very short lived. In some cases, it is so short lived that it is impossible to measure, and Streaming Current Analyzers can’t be used in those applications without chemistry modification or a change in coagulants.

Of course, there has to also be consideration given to mixing. If the mixing of the coagulant is poor, then the reading will be unstable if the SCM is mounted too closely to the injection point. In those cases, one should consider ways to improve mixing before deciding to move the sample point further downstream. This is because moving the sensor downstream often diminishes responsiveness. It can also leave the SCM setpoint more subject to variation and complicate PID control.

Ideally, the sensor will sample directly out of the rapid flash mix where the coagulant is added, or directly after a static mixer. Keeping the response time (or lag time) down to 30 seconds is ideal. But less than 1 minute is usually acceptable. How well a Streaming Current Aanlyzer will work with > 1 minute lag time longer is just going to depend greatly on water chemistry and type of coagulant being used. We advise contacting Chemtrac before making any decisions on where to install a sample point and permanently mount your sensor. This could save you thousands of dollars by not having to relocate the sample point later.
The first recommend step is to pour raw water that contains no coagulant through your sensor. If the sensor has already been running on treated water, it is advised to first clean your sensor as recommended in the manual beforehand. Its advised to slowly pour at least 2 to 4 liters of raw water through the sensor (smaller amounts can be used if the sensor was properly cleaned), and then adjust the gain for a reading of -150. Some customers may prefer a higher or lower value depending on how much response they see to their coagulant.

By adjusting the gain for a known reading on your raw water, you will know exactly what sort of reading to expect if you lose your coagulant feed. Also, you will have a clear idea of how much response you get to your treated water. For example, if raw water reads -150 and treated water reads -25, then you know that you are seeing around 125 unit response and an 85% reduction in your raw water charge reading. Anything better than a 50% reduction is good, and you want at least 100 units of difference between your raw water and treated water readings. If you results fall short of this, be sure to contact our application specialist to determine what next steps need to be taken.
When a new or recently cleaned Streaming Current Sensor is put into service, it can take anywhere from 5 minutes to 1 hour for the reading to stabilize. This stabilization time is often referred to as the “conditioning time”. This is because the probe and piston need time to fully condition their surfaces with the soluble and colloidal species in the water, and to reach an equilibrium with the sample. For various reasons, this can take longer in some cases, but usually requires less than 30 minutes.

Once a sensor has reached stabilization, the response to normal changes in water quality and coagulant dosing is much faster than the initial conditioning time and measured in seconds.
The cleaning frequency is going to be application dependent and determined by factors such as NTU, TOC, Iron/Manganese levels, and upstream additives (e.g. Potassium Permanganate can lead to sensor fouling). Many WTP’s can go weeks without needing to clean. In those situations, we recommend at least monthly cleanings. But in other cases, and especially in wastewater applications, more frequent cleanings will be required.

The best ways to determine when a cleaning is needed is to look for one of two things. The first is an unstable reading. A bouncy or erratic reading, where the reading changes rapidly from high to low in just a matters of seconds, is generally the result of a fouled probe or a probe with a loose fitting in the bottom of the probe. The second thing to look for is an unresponsive reading. This is often made evident by a slow drift in the pump speed that is not occurring with changes in water quality or flow. The following FAQ “How do I know my SCM is working properly?” provides more information on how to check response. If the reading is seen to be erratic or non-responsive, then a cleaning is recommended. Eventually, the customer will develop enough experience with the Streaming Current Sensor to determine a sensible routine cleaning frequency.
It is generally recommended to make a solution of Comet or Ajex, using 1 tablespoon per half liter of water. For tougher stains, especially arriving from iron/manganese, it is recommended to use a product like CLR or Hach Rover. It is not recommended to soak the probe and piston in cleaning solutions for more than a few seconds or minutes. And never use an acid to clean the probe.
To determine the ideal Streaming Current setpoint one first needs to determine the optimum dosage of coagulant. Jar testing is certainly a common method for determining the optimum dosage of a coagulant. We also highly recommend the use of Laboratory Charge Analyzer, like our model CCA3100, for quickly determining the optimum dosage of coagulant. Once the optimum dosage is determined, set the coagulant feed pumps to deliver that dosage

Wait for a few minutes after setting the optimum dosage for the Streaming Current value to stabilize. Once stable, the reading seen on the display can be used as the setpoint value by which to base future dosage adjustments. This reading can also be zero’d as discussed in the a following FAQ “What is the Zero Offset feature used for?”.
A common observation with streaming current controllers is that the setpoint does require adjustment from time to time. The changes to setpoint might be needed for various reasons, but the most common reasons have to do with changes in water chemistry (namely pH, alkalinity, and temperature). pH plays a very important role, especially when it comes to inorganic coagulants like alum. Other possible factors include adjustments to upstream additives, seasonal water temperature changes, large conductivity swings, and changes in water sources can all result in needing to re-optimize the setpoint.

Unfortunately, there are too many variables needed to make an accurate prediction of how often your setpoint will need to be changed. But generally speaking, a process that maintains stable pH (as measured at the SCM sample point) will fare better and require less frequent setpoint adjustments. Once again, we invite you to talk to our knowledgeable staff as we can provide a much clearer assessment once we have an opportunity to talk to you about your unique application details.
A useful feature of most Streaming Current Monitors is the ability to Zero the reading. This allows the user to make their ideal setpoint charge value equal to zero (0), which makes dosage adjustments easier to interpret. For example, if the ideal setpoint before applying the zero offset was -50, it might be difficult for an operator to interpret which way to adjust dosage if the reading went to -45. But if that reading of -50 was “zero’d”, then the offset reading would have gone from 0 to +5 when the true value went from -50 to -45. Seeing the positive number on the offset value gives a clearer indication that coagulant dose needs to be reduced (since the coagulant is known to drive the charge positive). Likewise, if the reading went from 0 to -5, it would be clearer from seeing the negative number that coagulant dosage needs to be increased.
Streaming current is more than a measurement of charge associated with suspended particulate. In fact, for many waters the streaming current reading is significantly more impacted by natural organic matter (NOM) than it is turbidity. This is because NOM carries a very high anionic charge in comparison to most particulate matter. So, even a small increase in total organic carbon (TOC) levels can cause the streaming current reading to move significantly in the negative direction. The ability to detect charge of both soluble and insoluble species is why streaming current meters are so useful in water treatment.
Streaming current detectors have even been shown to detect the presence of various chemicals that were accidentally introduced into a WTP’s source water. If your streaming current reading is going negative and turbidity is holding stable, it is advised to look at other measurements of water quality such as TOC, UV, BOD, and COD to determine if anything else is changing.
The simplest and easiest way to check to make sure your SCM is working is to simply make a 10 to at most 20% decrease in dosage for 5 minutes and note the response you see on your Streaming Current Monitor. That is an online verification test using your raw water and your coagulant, which is much more meaningful than most “verification” kits that will be discussed in the following FAQ “Do you have a calibration procedure for Streaming Current”.

For obvious reasons, some plants will not want to do the test described above. But the concerns of making a relatively small dosage adjustment of short duration should be weighed against the possible consequences of not doing these online verification test on occasion. Many WTP’s have assumed their SCM’s were working fine and only find out differently after their settled water NTU and filter effluent NTU started to climb due to a loss of coagulant feed.
Chemtrac does offer “verification solutions” that will clearly demonstrate the proper response of your Streaming Current Sensor where it matters the most, which is around neutral. We also offer ways to “calibrate” your gain setting to produce more consistent responses.

Chemtrac’s unique ability to verify the instrument response around neutral is important to understand because there are other suppliers who claim to have a calibration solution, but it’s just a solution with a very high dosage of cationic polymer which drives their reading well beyond the point of charge saturation. Streaming Current Analyzers will only go so far negative or so far positive before the reading flat-lines and becomes unresponsive to additional amounts of positive or negative charge. If you add enough polymer to a sample of water, it will send the Streaming Current reading to this max value and give a repeatable result, but it has no bearing on whether the sensor is working properly around a neutral charge.

A good analogy to help one understand our competitors calibration procedure better would be pouring in a 1,000 NTU standard into a turbidimeter that is designed to go no higher than 100 NTU, and then claiming that calibrating the turbidimeter to read 100 NTU using that 1,000 NTU somehow ensures an accurate or repeatable response at a value below 1 NTU. So, don’t be fooled, and definitely don’t pay good money for any calibration/verification kit that isn’t capable of checking the instrument response near neutral.
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