August 14, 2013
Liquid Handling Buying Guide
SelectScience.net has just published a very thorough guide for anyone looking at purchasing a new liquid handler.
You can also find many liquid handling product specs listed on their site by clicking here.
Of course, if you are budget constrained and need a great liquid handler at reduced pricing take a look at UsedLiquidHandlers.com
August 7, 2013
Lab Instrument Support Survey
New MVS Survey
Oh behalf of HTStec, The LabSquad is pleased to inform you that their latest survey titled "LAB INSTRUMENT SUPPORT STRATEGIES TRENDS 2013" is now underway.
"Proper maintenance of laboratory instrumentation is an important consideration to ensure that lab assets remain available to researchers. Minimizing downtime makes the research process more efficient. A variety of support options are available from original equipment manufacturers (OEM), small third party independent service organizations (ISO), large multi-vendor service (MVS) providers and internal support staffs. Understanding the needs of lab users is essential for service providers to ensure customer success."
If you count on your lab instruments being in 'research ready; condition, please take a moment and fill out this most important survey. JUST CLICK HERE
July 23, 2013
Motor Madness - Part III (...and final, I promise)
In the last two installments, we talked about simple DC motors and stepper motors. To recap, a DC motor is basically the simplest (think 'Lloyd' from the movie 'Dumb and Dumber') motor you can find. Simply apply voltage with sufficient current and it spins. You can reverse the spin direction by reversing voltage polarity, and you can control the speed by applying varying voltage levels or by sending short pulses of voltage. Stepper motors are a...'step up' (I hate puns) insofar as intelligence goes (think 'Harry' from 'Dumb and Dumber'). By which I mean, you can send them specific (countable) pulses and the motor will rotate in very predictable increments (steps). Steppers are natively 'open loop' but are oftem fitted with rotary encoders to provide position feedback. However...that position feedback is often an 'after the fact' reconcilliation on the number of steps commanded vs the number of pulses counted. It is not a 'monitor on the fly' feedback loop and that is by definition what a servo motor brings to the table.
In the most basic sense, a servo motor is a brushess DC motor fitted with a feedback sensor. The output of the feedback sensor is used to determine the final position of the motor. These devices can be very small (like hobby RC servos) or larger. In general, with increased size comes larger windings which enable more current and greater torque. Depending on the device the motor is attached to, you can expect to see a series of drive reduction gears or pulleys for even greater torque. Unlike hobby servos which have both gear reduction and circuitry embedded within their housings and use potentiometers for feedback, most industrial servo motors require a separate driver or control board that provides motor voltage and also monitors the encoder in real time. The image to the left represents a simple hobby servo which nicely illustrates the feeback loop concept. Both the input signal and the output from the sensor (potentiometer, in this case) are feed into a comparator circuit. Because the gearing is built in and known relative to the gear ratios, the comparator can essentially decide when the motor needs to be stopped in order to achieve the commanded motion (so many pulses should equal so much resistance).
The pulses sent to the motor are generally all the same voltage but number of pulses sent over time is what determines speed. This is called Pulse Wideth Modulation (PWM).
Troubleshooting a servo motor is not easy. If the motor and encoder are separate units, you can apply the rated voltage to motor (disconnect any pulley/belt or linkages first!!!). Encoders are a bit trickier and we will cover them in a future tutorial. You can try some basics like checking wiring connectors or blowing air the encoder to remove dust, dirt or grease. Beyond that...you will need to crack open the case and hook up a scope to see what the pulse train coming from the encoders look like. Most encoders are off the shelf devices and you can Google specs to compare with what you have. This will at least help you zone in on the encoder or the controller/board it is plugged into.
July 22, 2013
Motor Madness - Part II
Unlike a brushless DC motor which rotates continuously when a fixed DC voltage is applied to it, a step motor rotates in discrete step angles. Stepper Motors are manufactured with incremental steps per revolution of 12, 24, 72, 144, 180, and 200, resulting in stepping angles of 30, 15, 5, 2.5, 2, and 1.8 degrees per step. The stepper motor can be controlled with or without feedback.
Stepper motors work on the principle of electromagnetism. There is a soft iron or magnetic rotor shaft (rotor -= rotate...it spins) surrounded by the electromagnetic stators (stators = stationary...they're fixed locations). The rotor and stator have poles which may be teethed or not depending upon the type of stepper. When the stators are energized the rotor moves to align itself along with the stator (in case of a permanent magnet type stepper) or moves to have a minimum gap with the stator (in case of a variable reluctance stepper). This way the stators are energized in a sequence to rotate the stepper motor.
There are two basic types of steppers-- bipolar and unipolar.Unipolar
- A unipolar driver's output current direction cannot be changed.
- There are two sets of the coils for each phase in a motor.
- Only one set of the coils can be energized at a time.
- Each coil represents one phase.
- Driver's output current direction can be changed. 100% of the winding is utilized in the bipolar drive. That means the two sets of the coils in each phase can be connected either in series or in parallel to become one set of a coil
- Current direction changed from the driver creates another mechanical phase.
- The number of mechanical phases is always twice the number of electrical phases
- Bipolar drivers provide 40% more holding torque than unipolar drivers, but typically run at higher temperatures
For this last reason, proper heat dissipation is important with bipolar drivers. A bipolar stepper has 4 wires and Unipolar steppers have 5,6 or 8 wires. The rotor has a permanent magnet attached to it. The stator is made up of coils as shown in the image to the left. There are eight coils in this unipolar stepper motor. Every coil in the motor behaves as an electromagnet, when they are energized by electrical pulses. For this particular motor, the opposing coils are paired and each pair shares a common wire.You can see that there are five electrical conntections of the PCB (one common, and four to control each coil pairing).
Stepper motors tend to be less expensive than servo motors (more on servos in Part III), and they are easier to control due to the fact that their precise incremental movements do not require posistional feedback. Simply command this 'open loop' motor and the location is predictable. Now, if a pulley attached to motor shaft comes loose, or if a timing belt attached to the pulley were to lose a tooth due to wear, it is conceivable that the device being controlled could act in an unpredictable way (gets lost) and could fail (crash).
Stepper motor control circuits can be viewed with an oscilloscope.You would need to identify the driver chip or indexing controller being used and look at the pulse train (disconnect any pulleys first).with the motor attached. The motor itself can be tested with an ohmmeter. If you have a bipolar motor, place the ohmmeter between the positive and negative input terminals of each winding. The resistance of the two windings should be exactly the same. If not, the motor must be replaced. If you have a unipolar motor, place the ohmmeter between the positive terminal and the com terminal and then between the negative and com terminals. Do this for each winding. In each case, the resistance should be the same for all measurements; if not, the motor must be replaced.
July 15, 2013
Motor Madness - Part I
If it moves...it probably has a motor. There are a number of different types of motors within lab instruments and while repair or diagnosis of many of them are beyond the expertise even the most savvy field service technician, it is helpful to know a bit about them and what makes them tick (or spin).
The most common motors are simple AC or DC motors. As their names imply, each uses a different current scheme to achieve basic rotation but a simple brushed DC motor has five parts:
- Armature or rotor
- Axle (shaft)
- Field magnet
In many motors, the outer metal housing contains at least two field magnets (North and South).
The armature, also called the rotor as it rotates about the axel, is an electromagnet made by coiling thin wire around two or more poles of a metal core.
The commutator is a pair of plates attached to the axle. These plates provide the two connections for the coil of the electromagnet.
The commutator and the brushes enable for the "flipping" of the electric field" part of the motor.
Brushed DC Motors have two coils of wire around a rotor in the middle. Surrounding the coil are two magnets, both facing in the same direction. When the coils are facing the magnets, electricity flows into them. When electricity flows into a coil, it creates a magnetic field, and this magnetic field pushes the coils away from their magnets. As the rotor turns, the current shuts off. When the rotor has turned 180 degrees, each rotor faces the opposite magnet. The coils turn on again, this time with the electricity flowing in the opposite direction. This creates another pulse, pushing the rotor around again. The rotor has electric contacts on it, and there are small metal brushes that bump against the contacts. The brushes send in electricity, turning the motor on and off at the right times.
Operationally, all you need to do is apply the proper DC voltage at the nominally rated current and the motor will spin. For simple devices this can be done via an on/off switch.
A brushless DC motor has a permanent magnet on the inside of the rotor, such that its north and south poles are perpendicular to the axle. Coils surround the rotor. These coils function similar to a brushed motor in that hey give out timed pulses to push the magnet, spinning the rotor. Because there are no brushes however, the motor cannot control itself. Instead, it is attached to a speed controller ciruit, which gives pulses of electricity at a certain speed to control the motor. The faster the coils pulse, the faster the motor will spin. This is called Pulse Width Modulation or PWM (more on that in Part 3).
On a final note, other than brushes, there reall isn't much that can be easily fixed on a DC motor. For older devices that are no longer supported, you can find rebuild services that can repair toasted armature (more common on larger motors). The most tempting way to test a DC motor is of course to apply power...but please, if you do this make sure to disconnect the motor from any mechanical drive components (pulleys, bests, chains, linkages...etc) first. As always, if you choose to ignore this advice, please do not send nasty emails, legal notices or graphic images of your physical injuries...
Next Up: Part 2 - Stepper Motors
June 28, 2013
By The Book
Did you ever work with a field service engineer who was just plain awesome...someone who always went above and beyond to ensure your success? If so, you have probably asked yourself ''what would I do without them? ' Sadly, that hypothetical question, all too often, becomes reality.
For any number of reasons (some good, some not so good) people are transient. As the old saying goes, no one is truly irreplaceable, so the best protection vendors can provide for their customers is to ensure that more common procedures are documented. For example, irrespective of who is doing the work, a preventative maintenance procedure should always be the same. Each step, every tool, replacement part, lubrication or adjustment should be captured in a document that can be used to cross train FSE's so that your instruments always receive consistent maintenance.
Whether you are working with a new FSE to support a new install, or existing instrument don't hesitate to ask to see the procedure they will be following. Most vendors won't share all the details, but many will let you have a glance and most will provide checklist that highlights the work to be done.
If a vendor cannot produce documents for common procedures (like a PM). before they commence their work you should be concerned. I'm not saying that you are about to be mis-treated, however how can you be certain that the requisite work will be accomplished if there is no guideline? You wouldn't conduct an assay without a documented procedure and you shouldn't allow anyone to work on your instruments without one either.
If they can't show you 'the book', then throw the book at them!
June 21, 2013
Multi Vendor Service Webinar
June 20, 2013
Mike, Cancer & Chaos Theory
My friend and colleague Mike Williams was diagnosed with Neuroendocrine cancer. Also known as carcinoids, these slow growing tumors are often found in the digestive system (can also be found in the lungs and other organs) and are referred to as 'cancer-like'...but make so mistake, they are cancer by every definition of the word and those receiving a diagnosis similar to Mike's are often told to 'get their affairs in order...'
Unlike Russ, another friend of mine who lost his 2 year battle with a similar cancer last week, Mike was diagnosed over 6 years ago. Mike has endured multiple surgeries and chemotherapy regimens as well as a long list of experimental drugs and drug cocktails. Last month, he presented at the Midwest Lab Robot Interest Group meeting (LRIG) and spoke eloquently about the role automation and instrumentation has had on cancer patients from a first person perspective. His talk can be viewed by clicking here.
In his closing comments, Mike points out that what many of us consider to be routine or mundane activities have real world implications for patients. It's sort of like the butterfly effect... postpone an instrument service call or back order a critical component and you might delay an assay run that could yield novel data about a promising compound which could effect follow up studies, that then delays publication, resulting in missing a journal submission deadline that moves out the dissemination of clinically relevant info that might effect otherwise terminally ill patients...etc.
Mike is a shining example of perseverance, hope, faith and applied science. I am so happy to see him presenting and grateful that he could take the time to share his journey with us. I'll never look at a service request the same way again... Godspeed Mike Williams.
June 6, 2013
Power To The People!
One of the most challenging problems faced by field service techs and engineers is intermittent failures that appear to have no discernible root cause. Well…as least not an obvious one like a loose cable or belt. More often than not, the most common cause of such failures is overlooked…electrical power. Incoming AC (alternating current) power has been around so long that most of us take it for granted. So long as the lights come on, we assume all is well. That’s not always true.
In North America, most labs have either 110VAC (actually somewhere between 105-125VAC) or 240VAC (for larger instruments like freezers or floor mount centrifuges). The AC power that feeds most lab instruments is converted into DC power via the instruments internal power supply which also steps it down to power integrated circuits, dc motors, relays, solenoids..etc (generally in the 5-24VDC range). Power supplies are pretty robust devices that can provide constant, clean DC voltage, but like many things in life the quality of the output is a function of the quality of the input. Garbage in = Garbage Out.
Unlike DC voltage which if looked at with an oscilloscope would show a flat line, AC voltage is actually a sine wave and in most cases, the rated voltage of a circuit is represented by the average (RMS) of the voltages under the curve over time (usually 50 or 60 HZ or cycles per minute). Now, garbage might be a harsh term but what we are really talking about are several common problems;
Voltage Spikes – Sometimes called a surge, a result of incoming voltage exceeding the rated voltage by 10% or more. This typically happens when an inductive load (like a centrifuge) is turned off. The centrifuge pulls a lot of current and taking that load away (current) allows the voltage to quickly increase (ie, spike). If an instrument has a well designed regulated power supply then no problem, but transient spikes (think lightening) have been known to take out the best designed power supplies.
Voltage Dips – a temporary drop of more than 10% (ex: 120V * .9 = 108V). Probably not a killer, but what if your device is spec’d at 120V and the input line power is only 110VAC? Now with a voltage dip you are talking 99VAC … Some instrument power supplies have the ability to detect under voltages and report errors, many do not. And…guess what usually happens after a dip? You guessed it, a spike!
Noise – AC-powered devices can create a characteristic hum at multiples of the frequencies of the AC power that they use. Hums are commonly produced by spinning motor and transformer core laminations vibrating in time with the magnetic field. The noises can wreak havoc on under-voltage situations as they can temporarily cause an instrument on the hairy edge to work temporarily. Shut the noisy device off and the line dips down again causing the instrument to fail (or act really weird).
What to do if you suspect power issues? Well for starters, whenever an instrument starts to show ‘random’ failures;
- Have facilities verify incoming power. A digital voltmeter can be used for this, but make sure they are using the RMS (root, mean, square) setting to capture the average voltage. When in doubt, put a scope on it. Scopes can also show noise as well as nominal voltages.
- Isolate the instrument in question. Make sure there are no other devices on the same circuit.
- Put a digital or analog chart recorder on the circuit and monitor the line over several days. Sometimes called a strip recorder, the analog version looks like the lie detectors you see in crime shows. A needle draws on the paper producing peaks whenever it sees a spike or dip. Newer digital units do the same thing but are much less intimidating to less truthful members of society…
- Note the time that failures occur. Not surprisingly, spikes and dips tend to occur in larger facilities when people arrive at work, go to lunch, take breaks or go home around the same times. PC’s , HVAC, lights are turned on/ off – all in the name of conservation…the laws on unintended consequences.
- Plug the instrument into a line conditioner, then plug the conditioner into the circuit. Power conditioner are good for removing noise and higher-end models (don’t go to Home Depot for this…) offer some protection for spikes and under-voltages. Not to be confused with Un-interruptable Power Supplies (UPS) which offer a measure of time insurance in the event of a total power loss. Even basic UPS’ are available with spike and dip protection but even without they are still not a bad investment if you have dirty or unreliable incoming power and no easy way to fix it…
Net/net – don’t be so quick to blame an instrument for abhorrent behavior. Sometimes it is best to recall a bit of Shakespeare…”the fault dear Brutus lies not in our stars, but im ourselves (or our facilities).”
June 3, 2013
Good Reads about Multi-Vendor Support
Thought I would share a few articles and interviews that talk about Asset Management and Multi-Vendor Service support.
Next Generation Pharmaceutical-Outsourcing Asset Management, Bob Moore – GE Healthcare, interview
Lab Manager Magazine – The Evolving Service Model ; Good overview of service offerings from GE, Agilent, PE and Thermo Fisher.
BioScience Technology.com – Managing More Lab Assets
GEN – Lab-Asset Management Gets Smarter; older article (circa 2008) but shows that Asset Mgt within life sciences has been around for awhile.