Punt Blogger

Do You Have Any Blogging New Years Resolutions?

2010-01-09T08:27:00.000-08:00

The new year is here and in chatting with a lot of bloggers this past week I’m hearing a lot of optimism and planning going on when it comes to blogging in 2010.

Do You Have Any Blogging New Years Resolutions for 2010?

Would love to hear your thoughts on where you’ll be heading and what you’re planning?

My plans are coming along for punt Blogger. I’m planning on a review of the whole brand of punt Blogger in the coming weeks, a redesign (that will flow out of that), new features and levels on punt Blogger.com, a new E-book in the coming month and a lot more.

What about you?

The Blah Blah Blah Blogging Rules. F It.

2010-01-09T08:24:00.000-08:00

I’m having a rule-following problem. As in, don’t want to follow them.

Which rules? These ones:

Use snappy titles containing a question, the words “How To” and jarring adjectives. Do not be cute, arty, or poetic. Copy-write. Read the titles on the cover of The Enquirer or Cosmo and do what they do. Your title is more important than the post, itself.

Give advice. Provide value. Solve problems. Don’t talk about your cat or your sex life.

Make it scannable. Break up text with headers.

Make is scannable. Use lists.

Make it scannable. Use boldface and italics to emphasize your point.

Be brief, simple and stick to one topic. Your readers are only scanning it, anyways.

The Blogging Rules, Flouting Them, and the Faux-Rebellion.

Here is my confession: I’m a lit-on-fire blogger (who hates the word blog, cringes when I’m called a blogger, and resists the word “post”) but I don’t want to play by these rules.

I want to write wild, long, passionate, raw and real. I want to create art. I want to write words that land and burrow and inhabit my people. (I should just admit that I’m a wannabe poet and call it a day. Then no one would EVER read/scan my stuff. And so I blog.)

Here is my second confession: I adhere to the Gospel of Doowhatchalike. My titles are posts in and of themselves. I often write loooooooooooong pieces – sometimes 2,000 words or more. I insert my opinions and streams of consciousness and wackadoo digressions all over the place and they’re usually more interesting than the ostensible topic. And then I post pictures of my cleavage.

But just between you, me and the double D, I’m not a rebel.

I may have a vivid imagination and torrid/insane romantic life (thanks, vivid imagination!), but otherwise am so screamingly normal that it makes your normal tawdry. This is me: 9-5, kids, stability, friends, family, education, achievements, regular oil changes, a yard that doesn’t raise the wrath of strata, blah blah blah.

Why then, in my blog – my baby, my heart, my love, my creative offering to the world, my own thing – do I have to follow the rules? Why do you?

The Revolution Will Be Blogged

Recently, at my own site, I asked: Why do you blog?

The answers were many, varied, and invariably wonderful:

I blog because I love to write; blogging is just another form of expression for me. – Amanda Farough, Violet Minded

Though I may never become a writer who makes millions through my craft, blogging has given me the opportunity to affect the lives of others with my words. – Maven, A Fabulously Good Life

I blog because I’m the savior of the world and if everyone would just listen to me, we would all be better off, but then, I can’t even save myself sometimes so I guess that’s not true either.

I blog because I love run-on sentences.

I blog because the Infinite source of the cosmos calls me to it, that or is constantly warning me to stay away from it. Either way, I’m pretty bad at listening. – Steve, Life Change For You

I started blogging initially because it I was bored, dateless and cold on one January Friday night in Chicago. True story – Laura Cococcia, The Journal of Cultural Conversation

I am a glutton for personal development. whut.

I blog about it because I do my best thinking when I’m talking. I learn things as I explain them to others. I realize truth about myself, ugly ones and damaged ones and foreign ones, when I’m not stuck in my own head.

I blog because blogging is gangsta, and I got a gangsta lean. – Carlos Velez, Conscious Me (coming January 2010)

I needed a space where I could support my own interests, where I’m the Queen Of My Own Domain! It was also a challenge to push myself to try something completely new…to get unstuck and out of a rut. – Eileen, Blue Bird Luxe

I also consider it a creative act and a political act – any woman blogging now is raising a voice for all those womens’ voices which were silenced throughout history. And as the famous quote by Adrienne Rich states: When a woman tells the truth she is creating the possibility for more truth around her. – Lianne Raymond

…I blog because I want a revolution, I’m adverse to guns, and toddlers aren’t great at protest marches (unless they’re protesting the lack of third bowls of ice cream or fourth green bananas). – Arwyn, Raising My Boychick

To recap: we’re blogging for creative expression; to affect the lives of others; because the-cosmos-made-me or we’re bored and dateless and got a gangsta lean; for challenge; as a creative and political act (be the revolution), and lions-and-tigers-and-bears, OH MY.

Nobody said this:

To follow the rules

To do what everyone else is doing

To turn my blog into a cliché

To make money (whaaaaaa????? NOBODY? – okay, a few)

My point: blogging can be transformational.

You know why?

Because it is writing – and we might say, oh you don’t have to be a good writer to be a popular blogger, but for the most part that is a big wiggly lie – and we’re doing it daily.

Those two things, together, mean we’re thinking about THINGS and working through them. A-ha moments are practically guaranteed.

And then there are the people. Wow, the people. Blogging lets us find our people and that is a revelation. It is like coming home to a love-in, only everyone keeps their clothes on (usually) and talks pretty about thinky things. It is beautiful. It is soul food that doesn’t make you fat.

Transformation, community, freedom, creative expression.

That’s why some (most?) of us are blogging. We’re not looking for another set of rules to obey.

Nope. Not even one person jumped on the couch to scream “I LOVE THE RULES. Katie Holmes, Schmatie Holmes, I WANNA MARRY THE RULES!”

So WHY all the Blogging Rules?

So what’s up with the rules? Who made these rules anyway? Why do we need them?

Even more importantly – let me put my social science hat on here and run a really good query – where do they come from?

Dearest Reader, I knew you’d ask, so I did the research. And this is the answer:

F it.

That’s not a code and I’m not alluding to a bad word. That’s really the answer. That’s how people read online.

F for fast. That’s how users read your precious content. In a few seconds, their eyes move at amazing speeds across your website’s words in a pattern that’s very different from what you learned in school.

In our new eyetracking study, we recorded how 232 users looked at thousands of Web pages. We found that users’ main reading behavior was fairly consistent across many different sites and tasks. This dominant reading pattern looks somewhat like an F and has the following three components:

Users first read in a horizontal movement, usually across the upper part of the content area. This initial element forms the F’s top bar.

Next, users move down the page a bit and then read across in a second horizontal movement that typically covers a shorter area than the previous movement. This additional element forms the F’s lower bar.

Finally, users scan the content’s left side in a vertical movement. Sometimes this is a fairly slow and systematic scan that appears as a solid stripe on an eyetracking heatmap. Other times users move faster, creating a spottier heatmap. This last element forms the F’s stem.

That’s not reading. That’s scanning – that’s a person who ended up on your site thanks to Google, and who is searching for an answer to a question. A solution. Maybe even something to buy. And that’s where The Blogging Rules come from.

Readers read the headline, maybe the first line or two, and then scan the body of the piece. Hence: great titles, strong leads, headers and lists.

Blogging Rules: Your New Best Friend. Alas.

The rules aren’t random. They’re a guide to crafting effective online content that gets read (errr…scanned).

Larry Brooks, the writing guru behind the rampant writing usefulness that is storyfix (and he’s so much more than that, too – he’s in love with me although he doesn’t know it nor does his wife. Vivid imagination, say hey!) writes in his blog about the importance of following the rules.

As in: if you’re a writer, and you want to get published, you better learn the storytelling conventions and rock them out. To the letter. Or resign yourself to being an undiscovered ungenius.

The same is probably true with blogging. The rules are about how people read online. And you want them to read your stuff, right? I mean that’s why we’re blogging, yes?

My inner imaginary rebel just nodded, sighed and said F it.

________________________

PS – Want more on the rules? Here’s a quick, top ten list of good stuff you can find here at ProBlogger. (Ah-choo!)

Striking Findings from an Eye Tracking Study

Behaviors of the Blogosphere Study Results

What is a Blog?

18 Lessons I’ve Learnt as a Blogger

Writing Good Content

Post Length – How Long should a Blog Post Be?

Granular One Topic Blog Posts

Using Titles Effectively on Blogs

Scannable Content

Writing Blog Content – Make it Scannable

30 Bloggers To Watch in 2010

2010-01-09T08:23:00.000-08:00

1. Dave Navarro

Follow @rockyourday

Dave was featured as one of tomorrows star bloggers in 2008 and has continued to impress in 2009. His tenacity and hard work have helped cement himself as a leading blogger and coach. He has a truly impressive resume with guest posts on Copyblogger, two product reviews here on Problogger and joint ventures with other high profile bloggers.

2009 has been the year where he strategically built up his profile to become a respected member of the blogging community. In 2010, I expect he’ll be leveraging that profile to provide more awesome resources to help bloggers succeed. You can check him out at The Launch Coach and be sure to sign up for his advance discount list and for advanced notice of his More Buyers Every Month training.

Lesson from ReadWriteWeb: An Interview with Richard MacManus

2010-01-09T08:21:00.000-08:00

One of my new years resolutions in 2010 is to interview one blogger per week as a podcast. I’ll post most of these for members of the community at punt Blogger but from time to time will share some of them here on punt Blogger for all to hear.

Yesterday morning I had the privileged of speaking with Richard MacManus – Founder and Editor of the successful ReadWriteWeb blog.

Richard started ReadWriteWeb back in 2003 and has since grown it into one of the world’s largest blogs in terms of traffic, subscribers and most importantly influence. Richard has also taken RWW from a single author blog into one with at least 13 writers.

In this 45 minute audio podcast Richard shares the story of RWW and its beginnings, talks about the transition to a multi-author blog, shares some tips for new bloggers, talks openly about how RWW is monetized (including through advertising, publishing premium reports and running events) and looks forward at the future of publishing.

The interview also briefly features my 18 month old son who decided that Richard was someone he really wanted to speak with :-)

Richard’s one of the most thoughtful and insightful bloggers I’ve interacted with and has built a blog that reflects this. He majors on being constructive, insightful and useful and this podcast reflects that.

You can listen to this 45 minute podcast here or right click and save it to listen to it at your leisure.

While you listen be sure to surf over to ReadWriteWeb and follow Richard on Twitter and Facebook.

PS: apologies if there is an initial slowness in downloading but as you’d expect, there will be a bit of action on this podcast in the first little while after this post goes live.

Do Make Money Online Tips only Work on Blogs about Making Money Online?

2010-01-09T08:16:00.000-08:00

One of the common critiques that I’ve seen about sites/books/information product/blogs/courses/e-book about making money online is that its only those teaching how to make money online who actually make money online.

‘He only has a six figure income because he charges people to learn how to make a six figure income!’

This was one comment that someone made about another blogger recently. It sparked a chorus of other similar comments – people like to use that argument.

I understand this critique on some levels – there are quite a few bloggers out there who do only make money from make money online blogs and have not really had success in any other niche. While there’s nothing wrong with this – it obviously raises the eyebrows of some and makes them wonder if it’s possible to do it any other way.

There are also a lot of make money online bloggers making big claims and hyping up their own success – trying to get credibility in what is a competitive niche. This can distort the prominence and success of this type of blog and make it seem like it’s the only type of blog that can make money.

Can you only make money online by starting a make money online site and charging for the information?

I think it’s pretty evident that this isn’t true. While there are a few prominent examples of success stories in the make money online niche there are more many more people making a great living from blogs in other niches.

However many times these stories go untold because:

the blogger behind the site doesn’t have an avenue to talk about their success

they don’t want to talk about it – for fear of competition

they simply don’t want to be seen to be boasting or ‘tooting their own horns’

I hear from many bloggers in a wide variety of niches who are making a good living from their blogs who for one reason or another have not talked publicly about their stories.

Side note: On the flip side I also hear from a lot of ‘make money online’ bloggers who struggle to make any money from their blogs (it is nowhere near as easy as it might seem).

My Own Experience

I first started making money from blogging on a blog that had nothing to do with blogging or making money from blogs. In fact the first blog I experimented with making money on was a personal blog that talked about a multitude of topics. In time that blog did start to talk about blogging but it was far from solely a ‘make money online’ blog.

I then started a photography blog that aggregated camera reviews from around the web (no longer active) on that original personal blog’s domain. That blog became the biggest source of my full time income in the next year or two (it was around this time I hit the ’six figure income’ level).

Out of my experience with that blog (and others) I started punt Blogger.net to talk about what I was learning and share tips on how to make money blogging (in 2004). punt Blogger did end up growing to earn more than that original photography blog but it wasn’t for a year or so that it got established.

The original photography blog wasn’t a very satisfying blog to run and I ended up letting it die before starting my new Digital Photography School in 2006. DPS took a couple of years to really grow to a significant level – but today it is my main source of income. Traffic wise it does 5-6 times the traffic of punt Blogger on an average day and income wise it’s making significantly more than this site (I’d estimate that it’s 3-4 times as profitable as punt Blogger most months).

I share this story in an attempt to dispel the myth that to make money online you have to talk about making money online. Yes you can make money in this niche – but there are plenty of other niches where bloggers are making as much, if not more.

Do You Make a Secret Full Time Income from Your Blogs?

My story is not unique – there are many bloggers ‘out there’ who have built successful blogs that now sustain them full time financially. By no means are these bloggers in the majority (most bloggers make very little) but they are out there!

If you’re making a full time living from your blog I’d like to connect with you. In fact – I’d like to interview you.

I know for some full time bloggers the idea of sharing your story is something you’d rather not do (due to reasons I outlined above) – but if you are interested in sharing your story and have done so simply because you didn’t have an avenue to do it I’d really be interested to touch base with you to explore whether you’d be interested in being interviewed here on punt Blogger.

If you’re interested – please contact me through the punt Blogger contact form. Please include the word ‘interview’ in the first line of your email to help me make sure it gets my attention. It would also be helpful to have a link to your blog and a short description of it and your business model. I will keep these details private unless we mutually decide to do an interview.

I can’t guarantee to interview everyone who emails – but I hope to do as many as I can to highlight how blogs have become profitable in a variety of niches.

Why Running Surveys with Your Readers Rocks?

2010-01-09T08:11:00.000-08:00

In the last two months I’ve started using Surveys to get in touch with readers more and more.

Those of you who subscribe to the Punt Blogger newsletter will know this first hand because late last year you were invited to participate in one – but I’ve also run a couple on my photography blog that have been incredibly useful.

I’ve been running the surveys using SurveyMonkey (it is a little clunky but it is free for smaller surveys and not the most expensive option for larger ones).

I have found running surveys beneficial in a number of ways:

Getting in touch with reader needs – this is the most obvious reason to run a survey, they give you real insight into the needs, problems and challenges of your readers. The information I’ve gleaned from surveys in the last two months have provided me with a massive source of post ideas for the coming months!

Understanding who your reader is – some of the surveys I’ve been running have asked questions that help me not only identify the needs of readers but also have helped me understand what type of readers I have. I’ve asked questions about experience levels, demographics and other things that help me get a picture of what type of person is reading – again this helps shape not only content but many other aspects of a site.

Warm up Your List – up until recently I’d not been sending emails to the Punt Blogger newsletter list. Due to time constraints I’d let my email list go cold. Sending out a survey to this ‘cool’ list was one of the best things I’ve ever done – it not only helped me in the above ways – it helped me re-engage with old subscribers in a way that was not about promoting myself or any product but which was all about them, their needs, their challenges and their situation.

Build Anticipation – later this month I’m launching another E-book on DPS. As part of the process of creating anticipation of this E-book among my community I’ve been running a simple survey to get readers engaging with me around some of the topics of the E-book. The survey will not only help me make the E-book better, but in the introduction to the survey we’re letting readers know about the upcoming launch – something that plays an important part in building some good buzz and anticipation of the launch.

2009-01-13T20:44:00.000-08:00

Thermistors

NTC thermistor, bead type, insulated wires

Thermistor Symbol

A thermistor is a type of resistor used to measure temperature changes, relying on the change in its resistance with changing temperature. The word is a combination of thermal and resistor.

Assuming, as a first-order approximation, that the relationship between resistance and temperature is linear, then:

ΔR = kΔT

where,
ΔR = change in resistance,
ΔT = change in temperature,
k = first-order temperature coefficient of resistance,

Thermistors can be classified into two types depending on the sign of k. If k is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor, or posistor. If k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor. Resistors that are not thermistors are designed to have the smallest possible k, so that their resistance remains nearly constant over a wide temperature range.

Thermistors differ from resistance temperature detectors in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger temperature ranges.

B parameter equation

NTC thermistors can also be characterised with the B parameter equation, which is essentially the Steinhart Hart equation with c=0.

where the temperatures are in kelvin. Using the expansion only to the first order yields:

where
R0 is the resistance at temperature T0 (usually 25 °C=298.15 K)

Conduction model

Many NTC thermistors are made from a pressed disc or cast chip of a semiconductor such as a sintered metal oxide. They work because raising the temperature of a semiconductor increases the number of electrons able to move about and carry charge - it promotes them into the conducting band. The more charge carriers that are available, the more current a material can conduct. This is described in the formula:

I = electric current (ampere)

n = density of charge carriers (count/m³)

A = cross-sectional area of the material (m²)

v = velocity of charge carriers (m/s)

e = charge of an electron ( coulomb)

The current is measured using an ammeter. Over large changes in temperature, calibration is necessary. Over small changes in temperature, if the right semiconductor is used, the resistance of the material is linearly proportional to the temperature. There are many different semiconducting thermistors sizes ranging from about 0.01 kelvin to 2,000 kelvins (-273.14°C to 1,700°C).

Most PTC thermistors are of the "switching" type, which means that their resistance rises suddenly at a certain critical temperature. The devices are made of a doped polycrystalline ceramic containing barium titanate (BaTiO3) and other compounds. The dielectric constant of this ferroelectric material varies with temperature. Below the Curie point temperature, the high dielectric constant prevents the formation of potential barriers between the crystal grains, leading to a low resistance. In this region the device has a small negative temperature coefficient. At the Curie point temperature, the dielectric constant drops sufficiently to allow the formation of potential barriers at the grain boundaries, and the resistance increases sharply. At even higher temperatures, the material reverts to NTC behaviour. The equations used for modeling this behaviour were derived by W. Heywang and G. H. Jonker in the 1960s.

Another type of PTC thermistor is the polymer PTC, which is sold under brand names such as "Polyfuse", "Polyswitch" and "Multiswitch". This consists of a slice of plastic with carbon grains embedded in it. When the plastic is cool, the carbon grains are all in contact with each other, forming a conductive path through the device. When the plastic heats up, it expands, forcing the carbon grains apart, and causing the resistance of the device to rise rapidly. Like the BaTiO3 thermistor, this device has a highly nonlinear resistance/temperature response and is used for switching, not for proportional temperature measurement.

Yet another type of thermistor is a Silistor, a thermally sensitive silicon resistor. Silistors are similarly constructed and operate on the same principles as other thermistors, but employ silicon as the semiconductive component material.

Applications

PTC thermistors can be used as current-limiting devices for circuit protection, as replacements for fuses. Current through the device causes a small amount of resistive heating. If the current is large enough to generate more heat than the device can lose to its surroundings, the device heats up, causing its resistance to increase, and therefore causing even more heating. This creates a self-reinforcing effect that drives the resistance upwards, reducing the current and voltage available to the device.
PTC thermistors can be used as heating elements in small temperature-controlled ovens. As the temperature rises, resistance increases, decreasing the current and the heating. The result is a steady state. A typical application is a crystal oven controlling the temperature of the crystal of a high-precision crystal oscillator. Crystal ovens are usually set at the upper limit of the equipment's temperature specification, so they can maintain the temperature by heating.
NTC thermistors are used as resistance thermometers in low-temperature measurements of the order of 10 K.
NTC thermistors can be used as inrush-current limiting devices in power supply circuits. They present a higher resistance initially which prevents large currents from flowing at turn-on, and then heat up and become much lower resistance to allow higher current flow during normal operation. These thermistors are usually much larger than measuring type thermistors, and are purpose designed for this application.
NTC thermistors are regularly used in automotive applications. For example they monitor things like coolant temperature and/or oil temperature inside the engine and provide data to the ECU and indirectly the dashboard.
Thermistors are also commonly used in modern digital thermostats and to monitor the temperature of battery packs while charging.

Resistance Temperature Detector

2009-01-13T09:42:00.000-08:00

Temperature to resistance equation

The relation between temperature and resistance is given by the Callendar-Van Dusen equation

Here, RT is the resistance at temperature T, R0 is the resistance at 0 °C, and the constants (for an alpha=0.00385 platinum RTD) are

Since the B and C coefficients are relatively small, the resistance changes almost linearly with the temperature.

Platinum resistance thermometer

Notable characteristics

When pure, the metal appears greyish-white and firm. The metal is corrosion-resistant. The catalytic properties of the six platinum family metals are outstanding. For this catalytic property, platinum is used in catalytic converters, incorporated in automobile exhaust systems, as well as tips of spark plugs.
Platinum's wear- and tarnish-resistance characteristics are well suited for making fine jewellery. Platinum is more precious than gold. The price of platinum changes along with its availability, but its price is normally slightly less than 150% of the price of gold. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.
Platinum possesses high resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications. Platinum does not oxidize in air at any temperature, but can be corroded by cyanides, halogens, sulfur, and caustic alkalis. This metal is insoluble in hydrochloric and nitric acid, but does dissolve in the mixture known as aqua regia (forming chloroplatinic acid). Common oxidation states of platinum include +2, and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) species.The gold is removed from this solution as a precipitate by treatment with iron(II) chloride (FeCl2). The platinum is precipitated out as impure (NH4)2PtCl6 on treatment with NH4Cl, leaving H2PtCl4 in solution.

Applications

As a catalyst in the catalytic converter, an optional (though often mandatory by law) component of the gasoline-fueled automobile exhaust system (see "Notable characteristics" in this article).
As a catalyst in fuel cells. Reducing the amount of platinum required (and thus cost) is a major focus of fuel cell research.
Certain platinum-containing compounds are capable of crosslinking DNA and kill cells by similar pathways to alkylating chemotherapeutic agents. Cisplatin, carboplatin and oxaliplatin are licensed examples of this class of drugs.
Platinum resistance thermometers.
Electrodes for use in electrolysis and electrochemical measurements (e.g., the standard hydrogen electrode).
In the Clark polarographic electrode for measuring oxygen tension.
A wide range of jewellery
As a catalyst in the curing of silicone elastomers.
As a catalyst in glow plugs in some model engines.
Crucibles for high temperature melting of glass (for example) up to 1500°C better if alloyed with rhodium (10–40% of Rh).
In photography, it is sometimes used for archival printmaking. Platinum prints display a greater range of tones than other Black and White printing methods. Additionally platinum's chemical stability makes for extremely long-lasting prints. The disadvantage of this method, in addition to the high cost, is that platinum is less light sensitive and prints must be contact printed at the same size as the negative. Therefore, enlargements can only be made by making an enlarged negative.
In watchmaking, Vacheron Constantin, Patek Philippe, Rolex, Breitling and other companies use platinum for producing their limited edition watch series. Watchmakers highly appreciate unique properties of platinum as it neither tarnishes nor wears out and is ideal for gems setting. Vacheron Constantin started using platinum in watch production as early as in 1820. Today the company has a whole collection of platinum timepieces, Collection Excellence Platine, with the Malte Tourbillon Regulator and the Malte Perpetual Calendar Chronograph models introduced in 2007.

Resistance Thermometer elements

2009-01-13T09:12:00.000-08:00

Fig 1 : Resistance thermometer Construction

Fig 2 : Two wire configuration

Fig 3: Three-wire configuration

Fig 4 : Four-wire configuration

Fig 5 : Four-wire configuration

Resistance thermometer elements

Resistance thermometer elements are available in a number of forms. The most common are:
Wire wound in a ceramic insulator - wire spiral within sealed ceramic cylinder, works with temperatures to 850 °C
Wire encapsulated in glass - wire around glass core with glass fused homogenously around, resists vibration, more protection to the detecting wire but smaller usable range
Thin film - platinum film on ceramic substrate, small and inexpensive to mass produce, fast response to temperature change

Resistance thermometer construction

These elements nearly always require insulated leads attached. At low temperatures PVC, silicon rubber or PTFE insulators are common to 250°C. Above this, glass fibre or ceramic are used. The measuring point and usually most of the leads require a housing or protection sleeve. This is often a metal alloy which is inert to a particular process. Often more consideration goes in to selecting and designing protection sheaths than sensors as this is the layer that must withstand chemical or physical attack and offer convenient proces attachment points.(Refer fig 1)

Resistance thermometer wiring configurations

Two-wire configuration

The simplest resistance thermometer configuration uses two wires. It is only used when high accuracy is not required as the resistance of the connecting wires is always included with that of the sensor leading to errors in the signal. Using this configuration you will be able to use 100 metres of cable. This applies equally to balanced bridge and fixed bridge system.(Refer fig 2)

Three-wire configuration

In order to minimize the effects of the lead resistances a three wire configuration can be used. Using this method the two leads to the sensor are on adjoining arms, there is a lead resistance in each arm of the bridge and therefore the lead resistance is cancelled out. High quality connection cables should be used for this type of configuration because an assumption is made that the two lead resistances are the same. This configuration allows for up to 600 meters of cable.(Refer fig 3)

Four-wire configuration

The four wire resistance thermometer configuration even further increases the accuracy and reliability of the resistance being measured. In the diagram above a standard two terminal RTD is used with another pair of wires to form an additional loop that cancels out the lead resistance. The above Wheatstone bridge method uses a little more copper wire and is not a perfect solution. Below is a better alternative configuration four-wire Kelvin connection that should be used in all RTDs. It provides full cancellation of spurious effects and cable resistance of up to 15 Ω can be handled. Actually in four wire measurement the resistance error due to lead wire resistance is zero.(Refer fig 4 & fig 5).

Temperature Sensors

2009-01-13T09:07:00.000-08:00

Resistance thermometer

How do resistance thermometers work?

Resistance thermometers are constructed in a number of forms and offer greater stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a small power source to operate. The resistance ideally varies linearly with temperature.
Resistance thermometers are usually made using platinum, because of its linear resistance-temperature relationship and its chemical inertness. The platinum detecting wire needs to be kept free of contamination to remain stable. A platinum wire or film is supported on a former in such a way that it gets minimal differential expansion or other strains from its former, yet is reasonably resistant to vibration. RTD assemblies made from iron or copper are also used in some applications.

Commercial platinum grades are produced which exhibit a change of resistance of 0.385 ohms/°C (European Fundamental Interval) The sensor is usually made to have a resistance of 100Ω at 0 °C. This is defined in BS EN 60751:1996 (taken from IEC 60751:1995) . The American Fundamental Interval is 0.392 Ω/°C, based on using a purer grade of platinum than the European standard. The American standard is from the Scientific Apparatus Manufacturers Association (SAMA), who are no longer in this standards field.

Resistance thermometers require a small current to be passed through in order to determine the resistance. This can cause resistive heating, and manufacturers' limits should always be followed along with heat path considerations in design. Care should also be taken to avoid any strains on the resistance thermometer in its application. Lead wire resistance should be considered, and adopting three and four wire connections can eliminate connection lead resistance effects from measurements - industrial practice is almost universally to use 3-wire connection.

Advantages and limitations:

Advantages of platinum resistance thermometers:
High accuracy
Low drift
Wide operating range
Suitability for precision applications

Limitations:

RTDs in industrial applications are rarely used above 660 °C. At temperatures above 660 °C it becomes increasingly difficult to prevent the platinum from becoming contaminated by impurities from the metal sheath of the thermometer. This is why laboratory standard thermometers replace the metal sheath with a glass construction. At very low temperatures, say below -270 °C (or 3 K), due to the fact that there are very few phonons, the resistance of a RTD is mainly determined by impurities and boundary scattering and thus basically independent of temperature. As a result, the sensitivity of the RTD is essentially zero and therefore not useful.
Compared to thermistors, platinum RTDs are less sensitive to small temperature changes and have a slower response time. However, thermistors have a smaller temperature range and stability.