Streaming Current Sensor
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.
- 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
- 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)
- 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
-1000 to +1000
User-adjustable, 1 to 600x
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)
Sample Cell Type
External receiver, high flow
Quick-replacement cartridge with replaceable sleeve
Materials Contacting Sample
Delrin, viton, stainless steel
1 ea. shielded, 4 conductor, 22 AWG
Motor - RPM, Signal Health
110 VAC, 1 A, 60 Hz 220 VAC, 1 A, 50 Hz (optional)
NEMA 4X, fiberglass reinforced
34° - 120° F (1° - 49° C)
11.2” W x 9.2” H x 6.3” D
10 lbs (4.5 kg)
HydroACT 600 Analyzer
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
Up to 6 (some sensors may count as multiple measurement parameters; check with factory)
Up to 6 (750 ohm load); PID option will utilize 1 output
Up to 8 (250 VAC, 8A / 30 VDC, 8A)
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
1/4 VGA color display; or 5.7” touchscreen
Modbus (RTU, TCP), PROFIBUS, or HART
Minimum 4000 data points per channel without micro SD card (datalogging can be expanded with micro SD card)
Last 400 logged data points
micro SD Slot
1 (for data download & memory expansion)
4 (for digital comms, modem)
100-240 VAC, or 12 VDC
Nema 4X/IP65, ABS body, Polycarbonate lid
9.0” W x 9.3” H x 5.3” D (230 mm W x 237 mm H x 135 mm D)
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 Manuals||Version||Languages||Size||Date|
|DuraTrac 3 Operation Manual||1.8 MiB||02/11/2014|
|DuraTrac 4 Operation Manual||1.7 MiB||09/05/2014|
|DuraTrac 3 & DuraTrac 4 / Datasheets||Version||Languages||Size||Date|
|HydroACT 600 & DuraTrac 3 Datasheet||653.8 KiB||10/16/2013|
|HydroACT 600 & DuraTrac 4 Datasheet||711.3 KiB||09/05/2014|
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.
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?).
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.
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.
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.
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.
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.
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.
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 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.
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?”.
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.
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.
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’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.