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 © MasTec Ltd eNewsletter 2014

© MasTec Ltd  
October 2014

Circulation 15K



Category Focus

Sensors - Transducers link
Gauges - Encoders link
Signal Conditioners link
Signal Isolators link


Rotary gauges

Cable gauges

Laser gauges

Linear gauges

Flow gauges

Level gauges

Welcome to our Newsletter for October 2014

MasTec is now reselling Elster products in NZ direct from the factory in Europe. For all those metering needs ask our sales team for help. More on Elster next month.

This month our Product Category focus is:-

Sensors, Transducers, Gauges, Encoders

Signal Conditioners and Isolators

A total of 48 companies with a huge range of products.

We were going to include Cameras, Imaging and Motion this month but that is now next month as this present section is very large.

What are Sensors, Transducers and Gauges?

Sensors are usually binary devices, with a yes or no output. Many sensors have built in Hystersis with a dead band or zone so the sensor output will not oscillate if it sits on the threshold point. A sensor provides these types of answers: Is an object or a physical parameter in range or passed a threshold point.. Yes or No

Examples :

Thermostats Temp threshold reached yes or no
Inductive , Capacitive, Ultrasonic object detection yes or no
Pressure Switch Pressure treshold yes or no

Is an object or physical parameter in range?

Transducers measure a physical parameter over a range, and usually give a linear output based on this range.

Examples :

Temperature Transducers, Silicon, RTDs or PTs give a linear response, Thermocouples give a polynomial output over a range.

Others types of transducers are Pressure, Force, Linear, Light, almost all and any physical parameter.

There are many different types of transduction methods, converting physical parameters to electrical outputs.


Linear Transduction types

Resistive element that has a slider on it,
LVDT linear variable differential transformer
String to rotary converter Resistive or Encoders
Tape Encoder is a digital tape Trasnducer
And many other methods

Pressure and Force types

Strain Gauges on a diaphragm or element
Piezo Electric compression of crystals
LVDTs measuring displacemnt of a diaphragm or beam.
Capactivie two plates one moving with force.
And many other methods.

Gauges measure a physical parameter over a range, and usually give a linear output based on this range. This definitions sounds the same as a Transducer.

The difference usual is that the gauge is a complete device with power supply, display and a case, that givse reradings of the physical paramater that are calibrated and usable out of the box.

Sensors and Transducers usually all require powering and signal conditioners to make them useful

Hence the category Signal Conditioners

This is a huge category also and there are several companies that just specialise in this art. APCS, Dataforth to name two.

Additionally, almost all DAQ, PLC, PAC and Industrial manufacturers have a go at this product also. Some successfully, others not quite so.

The big thing about Signal Conditioning is that they actually allow building of a measurement and control system that will work in rugged, electrically noisy, poor physical environments.

For example : Low level Signal Conditioners woking with Thermocouples ( nanovolts to millivolts outputs ) are almost always ground isolated and have very high common mode rejections specs.

The reason for this is that if you are trying to convert a 1 millivolt signal on a thermocouple that may have a wire run of several meters through a 230 VAC or 415 VAC three phase area, you will need to clean out the capactively and inductively coupled AC and amplify the 1 millivolt up to either 4-20mA or 0-10 VDC outputs. This is tricky stuff. Often the noise level is thousands of times greater than the signal level.

Signal Conditioners do this sort of magic.

If you are powering Strain gauges, you need a DC excitiation voltage with better than 10ppm drift or better and very very low noise. Signal Conditioners have these built in and their error budgets overall, excitation and amplification can lead to confidence of +/-.05 to +/- .01 accuracy. Amazing results.

Remember there is no point in having a 16 bit ADC if your Transductions are only accurate to 1% because of noise, drift and ground loops etc.

In many cases of failed or flaky Automation and DAQ systems, can be traced to poor signal conditioning systems.

The last section of Signal Isolators is a similar theme.

if a cabling system is transporting a transducer or sensors signal trhough a long distance or even a short distance but a very noisy environment, the same game rules apply.

If there is noise, AC, Transient DC, Inductive from Motors, Radio signals from VSDs etc etc, all of this noise gets on to wires in some way and becomes part of the signal.

Differentially Coupled Signal Isolators can remedy most of these issues, as well as adding Filter Conditioners.

Another way for noise to get impressed on a signal cable is disparate Ground or Earth voltage levels between transducer or sensor to the measurement section.

In cases like this, a ground current flows around the cable causing errors.

Ground Isolators usually solve this problem very quickly.

Anyone working with 4-20mA systems very quickly learns all about these isolators.

When building DAQ systems, always use a common earth or ground point for the Analog Signalling Conditioners and the Measurement Systems..

If you can and you usual can, make the ground or earth for these conditioners on a separate cable. Do not include any digital systems like PC, PLCs, and PACs on that power cable.

Some other useful tips on reducing noise.

If you have a large load in your working environment that comes on and off, run a separate AC power cable to your Measurement or Automation system area. Do not assume you are getting clean AC power to your area. You can measure it and log it if you are concened.

If you are contolling VSDs and motors, only use shielded AC cables or conduits for the VSD and Motor power. Make sure they are a different AC phase set than your measurement and automation area.

If you can't do this, then run your measurement or automation system off an AC isolated UPS or AC Isolated Conditioner system.

Twisted pair cables were invented for a reason also, use them as much as possible (always). And if you can find twisted pair cables in a proper shield, like braided copper, use it on all your projects and systems.

Many USB devices provide a 5VDC output that can be used to power peripheral things. This is very common on DAQ and Automation products.

Do not use this 5 VDC line to power your measurement system, unless the USB device generates the 5VDC internally for you.

If the 5VDC comes through the USB cable powering the device, all you will get is the Switched Mode Power Supply of the PC, Laptop, PAC, PLC etc and they are usually very noisy.

If you need clean DC, get a linear power supply, not a switched mode PSU.

If you only need low power pure DC for powering devices with say 0-100mAs at different voltage levels, say 0-5, 0-10, maybe 0-1 VDC, then get a good quality USB DAC unit with multiply outputs. It may seem like a very expensive theng to do, but you will get 4 or 8 perfectly clean programmable DC outputs that will make your life oh so much easier.

Remember, your measurement and control system results and success, is tied very very tightly to your sensors, transducers, gauges outputs.

You have control over these sections and there is a little bit of art involved in all of this.

As it is a digital world now, not all enegineers have played with Analog enough, to get a feel for all of this art and rules.

Signal Conditioners and Signal Isolators can make a big problem disappear very quickly.

Do some reading if you are taken by all of this and if you get stuck, email MasTec for some help.

All the best with your measurements with Sensors, Transducers adn gauges.

NI's Test & Instrumentation Newsletter link

USA Signal Conditioner Company - Dataforth Interest

Australia Another Conditioner Company APCS Interest

German Precision Transducers- Jumo Interest

Swiss Precision Encoders Micronor Interest

French Precision Linear tape gauge Belval Interest

USA Sensors Transducer & Gauges Omega Interest

Belgian Precision Transducer BCM Interest

USA Cable gauges Unimeasure Interest

Italian Largest manufacturer Sesnors Infra Interest

USA Rugged Precision Transdcuers Alliance Interest

USA Precision High Frequency Cap Gauges Lion Interest

USA Linear & RotaryTransducers P&G Interest

Germany Colour & Distance Detectors Eltrotech Interest

German Best Coating Thickness gauges KD Interest

Raspberry PI + MCC DAQ - MCC View


Newsletter & Canbus Devices - ICPDAS View

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LabVIEW Training Courses - Link

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