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November, 2011 4
Visual Beacon/Cellular Alarm Transmitter
Ringback in Ultrasonic Level Sensors
Tech Tip, Why use Temperature Transmitters
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ECD Analytical Instruments


Electro-Chemical Devices (ECD) has a wide variety of liquid analytical instruments that can be used throughout the waste water treatment cycle. These include the more familiar measurements such a

FCA-22 Free Chlorine analyzer

s pH, ORP, and dissolved oxygen. In addition, ECD now has on-line instruments that measure many other parameters that are becoming more of a concern to operators. These include ammonium, nitrate, phosphate, phosphorus and free and total chlorine.


ECD Hyrda nitrate sensor
Hydra Nitrate sensor

The Hydra Nitrate Sensor is designed to monitor the nitrification process directly in the aeration basin or clarifier of a Waste Water Treatment Plant. The Hydra uses ISE technology to measure the Nitrate and Chloride. Compensation for the chloride ion interference on the nitrite electrode is performed automatically in the Hydra C22 analyzer. It is also available with an optional pH sensor.


 Click for more info on ECD analyzers

Visual Beacon/Cellular Alarm Transmitter

The SmarteLight is a new patented product from OmniSite which notifies you via email, text message, or phone call whenever you lose power to your pump station, or your alarm light is illuminated. This simple device can be field installed in minutes. Once installed, the SmarteLight works like all other OmniSite products, providing alarm history and configuration ability from the OmniSite GuardDog interface.


How the SmarteLight WorksOmnisite Smartelight


The SmarteLight is installed at your equipment and sends a wireless signal to the local cellular tower. That signal is bounced to OmniSite's web interface, where customers can log on - any day, any time, from any computer - and see how the equipment is operating.


A "call out" list is set up online, so that when an alarm is triggered at your equipment, identified operators are contacted immediately. Because OmniSite engineers recognize today's fast-paced busy world, that notification comes by way of text message, email or call to your cellular or hardwired phone.

More info on Omnisite SmarteLight



  Ringback in Ultrasonic Level Sensors


One of the more common causes of ultrasonic level sensor errors is a phenomenon known as ringback. Ringback is an installation problem that gives the customer a false high reading or alarm.


Since the ultrasonic transducers use a sound wave to calculate the distance to the level, they need to vibrate internally to create that sound. The transducer receives an electrical pulse from the transmitter causing the transducer to vibrate. When the electrical pulse has ceased, the transducer continues to vibrate. This continued vibration is ring down. During this period of time known as ring down, the ultrasonic system is unable to measure. Basically, the sensor is still ringing when it is trying to listen for a return echo.


Ringing can be prevented by following a few installation guidelines:


  1. Do not over-tighten the transducer. By over-tightening, we cause the transducer, coupling and mounting device to vibrate, causing extended ringing. This rule applies to both thread and flange mount transducers. You should tighten a transducer only finger snug where possible according to the area codes.
  2. Use a non-metal mounting material. Plastic or rubber does not ring as well as metal. By placing a non-metallic coupling on a thread mounted transducer or inserting a non-metal gasket on a flange mounted transducer, we can reduce the ringing.

Temperature can add to this problem. When installing a transducer in an area where there will be temperature swings, it is even more important to follow the mounting guidelines. As temperature decreases, the mounting becomes tighter as the material shrinks. This also can increase ringing.


For more troubleshooting tips with ultrasonic level sensor, take a look at the following video.

Siemens Hydroranger Troubleshooting video
Siemens Hydroranger Troubleshooting video


Tech Tip

What are the advantages of using a temperature transmitter over direct wiring a sensor to a PLC or DCS?


Cut Wiring Costs

Direct wiring sensors to a control system requires the use of sensor extension wires, which can be three times more than the common shielded copper wire used for a temperature transmitter's 4-20mA signal.

 Temperature transmitter 1A

Protect Signals from Plant Noise

In a direct wiring scheme, the low-level signals generated by an RTD (ohm) or thermocouple (mV) are particularly susceptible to the signal degrading effects of RFI/EMI. A temperature transmitter converts a sensor's low-level signal to a high-level analog signal (typically 4-20mA).


Stop Ground Loops

Make sure to choose an isolated transmitter. Input/output/power signal isolation protects against signal inaccuracies caused by ground loops. This is important even when using un-grounded thermocouples because their insulation will eventually break down.

 Temperature transmitter 2

Reduce Hardware Costs

With direct wiring, it is necessary to match the sensor type to input-specific DCS and PLC input cards. Sensor  input-specific  cards usually cost a lot more  per point than a 4-20mA input card.


Enhance Accuracy.

A microprocessor based temperature transmitter can be scaled over a wide or narrow temperature range. The accuracy of Thermocouple or RTD input cards is a percentage of the entire temperature span. You won't get very good accuracy if you want to measure a span of 100 deg F on an input card with a range of -200 to 1,500 deg F.


Click for more info on Signal Isolators