April 29, 2014 by Kevin Keras
Okay, so several of you have gotten impatient and sent me emails asking for the solution to the plate sealer mystery in my last post. As is often the case, the answer was simple but it was not obvious...a perfect storm of causes, if you will.
Let me cut (no pun intended) to the chase. The major factor was AC power...or lack thereof. Although the measured power coming into the unit was within spec for the instrument (112 VAC), the user also had a JunAir compressor on the same circuit...as well as a large refridgerator and a centrifuge. The combination of the sealer holding temp, the JunAir running almost continuously (due to a slight leak), the fridge compressor running and the centrifuge...centrifuging, resulted in a transient line voltage drop down below 100VAC. This was only measurable using a chart recorder which monitored the true RMS voltage. While the electronic display of the sealer operated and made it appear that the sealer was functioning, the timing of the pneumatics was not correct. The cutting bar would advance but retract before cutting action could take place. Because the JunAir runs quietly, it was difficult to see that it was pretty much always running due to the leak. We believe the fridge compressor kicking on while the compressor piston was the bottom of it's stroke is where the power drain occurred.
Isolating the sealer and the JunAir (fixed the air leak) from the circuit in question resolved the problem.
Chalk one up for the "doh!" list.
April 1, 2014 by Kevin Keras
"Ruh-Roh Shaggy!" as Scooby Do might have said when faced with a recent problem we encountered with an ABgene ALPS 3000 sealer.
A customer had two units that operated pretty much 24/7. One unit had tape seals while the other had foil seals, and it was not uncommon to switch between the two.
Iniital failure reports centered around a error message "Not Down." This was pretty simple and invovled the front access door switch. Users like to look inside the instrument as it was operating, so they would tape the switch closed. Occaisonally, the tape would expand and allow the switch to change states. A simple closing of the door and press of the e-stop button would reset the error and allow operation to continue. But, that was not the end...
Soon thereafter, additional calls for help were placed as the instrument would no longer cut seals. The cutting bar which is pretty beefy would only slice through a small portion of the edge of the seal, but never fully perforate. The unit in question was pulled for depot repair and of course upon power up, it ran fine. In fact, it sealed over 50 plates without error. The cutting blade was adjusted and another 50+ plates were run without fail. The unit was returned, but just to be on the safe side, we brought along another identical unit to run side by side with the clients unit.
Onsite, the unit ran great for several hours...then same problem. Our FSE's checked air (80PSI from a big honking JunAir compressor), and AC power...fine. The customer's plate were polypropylene and the temp was set at 167C...a little high, considering polypro has a melting point of 130C. Nevertheless, this is temp the customer had been using prior to failure with no issues.
The solution was simple...but not obvious. Care to venture a guess?
March 24, 2014 by Kevin Keras
A Simple Solution For Older XP Based Instruments
Okay, this time we really mean it! Microsoft is getting really serious about killing Windows XP on April 8th, 2014. Don't worry, no one from the NSA will be showing up with a search warrant on April 9th (...but, you never know). Well, what does this really mean for labs with Win XP PC's? Most IT departments have already made the mandate that Win 7 is the preferred OS for new PC's and many manufacturers have been making sure their software is compatible. But, as we all know, some instruments will be orphaned. That is to say, for a variety of reasons, manufacturers will not be updating software of older XP based instruments. Most labs that I have visited are getting around this in the short term by keeping Win XP PC's off the internal network and sneaker-netting data to a central network location via USB keys. Not ideal.
Below is a simple way to get the data flowing without manual intervention and protecting the integrity of the internal network. Note - this is not the only way, but it is a pretty robust solution.
Here's what you will need;
- Windows XP PC - connected to the instrument (usually USB or RS232) and one Ethernet port. Depending upon the age of the instrument, this PC may be a full tower (big) form factor which takes up a lot of bench space.
- Windows 7 PC - with two Ethernet ports, one of which will be connected to the internal network. You could use a laptop if it has both wireless and hardwired Ethernet (but, since many IT groups really frown upon wireless connections to the internal network, this example will only over desktop PC's). If your instrument PC has a compact factor (size) try to select a PC that is similar in size. It will make for a more tidy installation. You will only need one monitor/keyboard/mouse when you are done, so if the new Win 7 PC has these you will keep these and ditch the ones from your Win XP PC (see below).
- KVM Switch - this will allow sharing of one monitor, keyboard and mouse between the two PC's Be sure that your Win XP PC mouse and keyboard are USB. Some older PC's used the old PS2 style connectors. If this is what you have, ditch them and use the keyboard and mouse from the new Win 7 machine.
- Your IT Support Guru - don't go this alone. If you screw it up you will have to involve he/she to get it resolved so better to keep them on your good side. Besides, this is what they do for a living...you wouldn't like it if they tried to optimize your assays, now would you?
1) Place both PC's next two each other. One PC (Win XP) should be connected to your instrument already, just verify that it is working. The other (Win 7) will be connected to the internal network - make sure that it is working and connected to the network.
2) Plug the Ethernet crossover cable into the Ethernet port of the Win XP PC and the open Ethernet Port of the Win 7 PC.
3) Okay, now here is where the IT Guru comes in handy (remember to complement your guru and have Skittles and Redbull on hand). You are going to want to have Big Bang Theory configure the IP addresses and subnet mask of the two PC's to create a simple peer to peer network. Your IT Guru will know which Ethernet port to muck with on the Win 7 PC such that you don't screw up your network connection. BBT will also need to make sure that TCIP is enabled. EXAMPLE ONLY - LET YOUR IT GURU DO THIS...
Computer 1: 192.168.1.100
Computer 2: 18.104.22.168
The subnet mask entry must also be identical on both machines.
The Domain or Workgroup must also match between the two machines
4) Disconnect the monitor. keyboard and mouse from the Win XP pc and discard them. Connect your Win 7 PC keyboard, monitor and mouse to the KVM box. Most KVM devices have two sets of connections that go the separate PC's and just connect your monitor, mouse and keyboard to it. Pretty straight forward. A hardware button allows you to switch between PC's.
5) When finished, it would be preferable to label each PC and stack them on top of each other to conserve bench space.
6) Have your IT Guru look at where you are storing data Files on the Win XP PC. He/She will need to create a new location on the Win 7 PC and change your instrument programs to start saving data at this location. The data now residing on the Win 7 PC hard drive can now be mapped to your server.
1) Many lab instrument manufacturers use Dell PC's as their controllers, probably because they got a great deal on pricing and consistent quality/configurations. I have seen many an IT department specify Lenovo or HP PC's for their internal networks. Although the specs may look identical...strange things can happen. Most manufacturers will not support (or at least spend a lot of time with you) troubleshooting problems on other brand name PC's. Caveat emptor.
2) When maintaining older instruments, the most oft overlooked component is the PC. This is especially true if you have misplaced any critical instrument installation disks or license into. As long as you are planning to use an older PC, it is imperative that you not just back up the hard drive, but actually image the disk (re: Symantec Ghost). In a pinch, you can still replace a bad hard drive in an older PC and re-image the disk.
August 14, 2013 by Kevin Keras
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 by Kevin Keras
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 by Kevin Keras
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 by Kevin Keras
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 by Kevin Keras
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 Kevin Keras
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 by Kevin Keras