McNab Model HSD Back Scatter Yeast Analyzer

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For automatic and continuous real-time unattended monitoring of suspended solids concentration in liquid process vessels
  • Model HSD-A for High Concentrations
  • Model HSD-B for Low Concentrations
  • Model HSD-F for Fluorescence
Technical Papers/News Releases:

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  • Single head construction.
  • No air service required.
  • Rugged design is ultra-sealed.
  • Sensor assembly prevents particle build-up problems.
  • Automatic correction; quasi-double beam design.
  • Widest concentration range available.

How It Works

product_HSD_optical_tank_meas.JPG (77004 bytes)Consisting of a heavy-duty stainless-steel probe assembly and a remote indicator/controller cabinet, the Model HSD measures suspended solids content or fluorescence in process vessels.

The HSD probe assembly contains a combination detector unit, a sensor assembly and McNab's exclusive modular optical cell. The probe assembly mounts directly in the wall of the tank being monitored and the process liquid passes in front of it. The parameter is measured by passing a light beam into the process liquid and measuring the light scattered back to the probe. The light back-scattered (or fluorescence) to the detector is proportional to the signal of interest in the liquid. The signals are then sent to the indicator/controller cabinet.

The indicator/controller cabinet contains the modular electronic circuitry necessary to process the signals, to display the readings, to input desired set-points, to indicate alarm levels and to operate alarm relays. It also has continuous output for proportional control connections.

Because the probe assembly is vessel-mounted, without the need for the measuring beam to go across the process fluid, two heads are not necessary

The HSD provides immediate measurements at operational pressures and temperatures. Errors potentially caused by sample temperature and/or pressure variations are avoided, as are compromises normally required of off-line sample lines.

The optical window can be visually inspected anytime without vessel drainage. McNab's unique modular optical cell can be quickly hand-removed for off-line inspection, pressure test or replacement of the unit and/or to inspect the wetted surface. This design has effectively eliminated the measuring problems often caused by glass fogging, condensation, power and/or temperature fluctuations, or light-source bulb aging.

The Model HSD uses the very latest optical technologies to provide stable, low-noise signals across the range of light used for measuring.

Model HSD photometric analyzers measure process liquids in tanks with:

  • 5 Angle Of Presence
  • 0.1% Repeatability
  • Automatic Color/Parameters of Interest Compensation
  • Linear Output
  • Sanitary Sensors Prevent Particle Build-Up Problems
  • Time-Proven Design; Thousands Of Modular Optical Cells Installed Since 1960

No Standardization Required

product_HSD_sus_solids.jpg (26417 bytes)The HSD achieves measurement stability of 0.5% per year, allowing maintenance-free operation. This is made possible by a matched signal verifying module (SVM), with 100-megohm input impedance. This eliminates drift, so there is no need for constant restandardization. The SVM also corrects for any variation in sensor cable length, so nearby electric interference does not affect operation, even at cable distances of 600 feet (180m).

Advanced Optical and Electronic Design Provide Greater Range

The HSDs electronics have been specially designed so that the digital meter readings can be adjusted to fit parts-per-million (ppm) units.

The HSD/B operates on the reflection principle. The formula is:

Reflectance = Sample divided by reference

or in the HSD/A diffuse reflection, and this formula would be:

Log X 1 divided by reference

Continuous Accuracy Verification

product_HSD_alarm.jpg (36535 bytes)The HSD features McNab's exclusive lens fog alarm transmitter. This unique feature verifies accuracy of the analyzer by continuously monitoring the modular optical cell against the fogging effects of moisture.

An alarm system is contained within the indicator/controller cabinet to advise plant personnel when measuring accuracy is in danger of being compromised.

When the moisture removal system has reached the end of its useful life, or has been otherwise disturbed, an alarm will be indicated on the remote panels and may be coupled in to the 4-20 mA loop to signal the console of lens fogging.

This feature assures accuracy of the readings and helps reduce preventive maintenance requirements.

Comparing other photometric instruments to McNab

product_HSD_compare1.jpg (29629 bytes) Particles settle in sensor, obscuring detector.
product_HSD_compare2.jpg (33224 bytes) Sensor assembly acts as umbrella, preventing detector from sensing actual conditions.
product_HSD_compare3.jpg (32255 bytes) Sensor assembly "ledge" allows particles to collect, preventing back-scatter signals from being sensed.
product_HSD_compare4.jpg (31928 bytes) McNab sensors read actual conditions because particle build-up problems have been address in system design.

McNab Photometric Analyzers

Other McNab instrumentation is available to provide photometric analysis of such items as particle size and/or concentration using monitors that measure using nephelometric (scatter) and forward-scatter technologies for the measurement of low-level particles (NTU, PPM, EPA, etc.) as well as high-level chemical concentration, optical density and others. 

About McNab

McNab, Inc. is located in metropolitan New York City. Our offices in Mount Vernon, New York include our research & development laboratory, design engineering department, modern manufacturing plant and automatic testing facilites to evaluate our products.  McNab's Quality Assurance Process meets Mil-I-45208.  We also maintain an engineering and parts facility in Europe.


Model HSD
Principle of Operation: Indication of back-scatter readings to determine solids concentration.  Cell viability correction available.
Range: 0 - 60% cell concentration.
0 - 200 million cells/mL.
0 - 2000 fluorescent units.
Linearity: Typical 1% or better.
Ambient Conditions: 32 - 105F (0 - 40C), 0 - 100% relative humidity
Recorder Output: 0 - 1 mA, 0 - 100 mV, or 0 - 10 VDC selectable
4-20 Output: Two-wire, ground isolated powered or 20 mA is fullscale, 4mA equals zero, 36 volts max.
Alarms: Two independent adjustable set-point alarms; two relay closures, 5PDT, 5A resistive, 250 VAC max.
Built-in test and fault-isolation: Alarms, relays and 4-20 trip when bulb failure, obscurred windows, or power loss detected.
Housings: NEMA 4X (watertight)
hinged door W13" x H 16" x D 7" (33 x 41 x 18 cm) for wall mounting, or semi-flush
Weight: 25 lb./11.3 kg
Probe Assembly
Range: Follows indicator.
Material: Stainless Steel, ASTM 316L/DIN 4435, other materials available.
Optical Cell Window: Tempered borosilicate, Vitreous silica, TFE 3/8" to 1" (10 - 25 mm) thick (application dependant).
Optical Cell Seals: TFE, Ethylene propylene, Buna N, PFE, fluoroelastomer butyl (application dependant).
Interface: Sanitary (tri-clamp) ferrule.
Operating Pressure: 150 psig, 10 bar, (Contact factory for higher ratings.)
Operating Temperature: 15 to 225F (-10  - 115C).  Up to 480F (250C) with air purge.
Enclosures: NEMA 6 (submersible)
Separation from indicator: 600 ft. (180 meters).
System Test: Front panel push-to-test.
Accessories: Extensive users manual, regulated power supply.
Service: Commissioning, preventive maintenance, and filter selection laboratory work-up.
System Calibration: Multi-point polymer bead, formazin yeast or diatomaceous earth.  Custom calibration available.
Specification may be changed or improved as necessary.

383-2 East 29th Street | Buena Vista, VA | USA 24416-1293

540.261.1045 voice | 540.261.1268 fax |

Copyright 1999 - 2010  McNab, Inc. All Rights Reserved.  Last modified: 08.12.2010

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