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Application Notes, FAQs & Glossary |
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 | Application Notes
The variety of uses for the Lee LPV Pumps is almost limitless. However, the majority of uses follow one of the three following examples.
Direct Aspirate and Dispense
In this mode, a tip or tube assembly is connected directly to the pump. If the pumped fluid is only a transport medium, the entire pump and tube system is filled with it. Other times, the pump itself has only air in it, and the sample aspirated only contacts the tip or tube set. A third method uses an inert transport fluid, where the sample only contacts the tip and tube. The contact interface with the transport medium is flushed out and replenished with fresh fluid when necessary.
Pump Connected with a Three Way Valve
This type of operation uses a single, three-way valve as a means of controlling the pump flow. The common port is connected to the pump, and the other ports can be connected to either the dispense tip or the reservoir. A benefit of this type of control is the simple control circuitry, as well as the close fluidic coupling of the reservoir and dispense legs. Most syringe pump modules operate in this manner.
Pump Connected with Two Two-Way Valves
This connection scheme uses two, usually Normally Closed two way valves to control the pump flow direction. All standard configuration Lee LPV Pumps have two ports on the port head which may be utilized. Alternatively, an external tee can be used where appropriate. While slightly more expensive to construct, this dual valve mode offers more control over the flow stream. The valves can be made to be absolutely "closed center", unlike the three-way valve, which may have some volumetric switching error. This is usually the most precise way to operate the pump.
Frequently Asked Questions about Lee LPV Pumps
1. What are the safe operating temperatures?
All motors on our pumps have Class B insulation, which means a 130°C (266°F) rating. This winding temperature will only be achieved under very strenuous operation or at high ambient temperature. If this comes into question, monitor the motor case temperature. It should be held under 90°C for safety. If the motor case temperature is expected to exceed 60°C, measures should be taken to prevent injury from skin contact. The rest of the pump components will withstand operating temperatures from 20°C to 75°C.
2. What can be done to reduce motor heating?
Many drive modules have a feature which allows the current to be reduced when the motor is inactive. This reduces the power dissipation when the motor is at rest, without danger of position loss. Reducing the duty cycle can also be employed to reduce heating. Heat sinks can be employed to help extract the additional heat from the motors. Consult with Lee Company Sales
or Application Engineers for further information on this subject.
3. Can special lead wires be obtained?
Yes. Many of the pumps we sell have special lead wires and connector sets to connect directly into customers' systems. The Lee Company is committed to providing whatever connection the customer needs, or will obtain the necessary equipment to enable this. We have long-standing relationships with all major connector manufacturers.
4. How long can the lead wires be made?
While theoretically the leads can be as long as any spool of wire, practically we recommend limiting the length to two feet or less. While they can be accommodated, leads longer than two feet can present handling and packaging problems. Especially long leads may need to be made larger gage to reduce losses, and this may present connection problems at the motor.
5. Can special volume ranges be obtained?
Yes. We currently manufacture a family of products that covers most volume requirements, but will consider any volume request.
6. What about special fluidic connections or head designs?
We have the capability to make almost any configuration that can be imagined. We have made parts with special fittings, port orientations, internal geometries, and materials. We will work with customers to provide whatever configurations are needed.
7.Are any other wetted materials available?
Our standard wetted materials are the YTZP ceramic of the piston, the UHMWPE of the seal, and either PEEK or PMMA (acrylic) for the port head. Almost any other material can be used for the port head, and several other options exist for the piston and seal.
8. What is a Unipolar Stepper?
The simplest type of stepper is the unipolar motor, shown below. It is referred to as a unipolar drive because the current can only flow in one direction through any particular motor winding. A bifilar, or dual wound coil must be used since reversal of the stator field is achieved by transferring current to the second coil. A drawback of the unipolar drive is its inability to utilize all the coils on the motor. At any one time, there will only be current flowing in one half of each winding, which is fairly inefficient.
To realize the full benefits of the LPV pump's higher performance and efficiency, a bipolar (bi-directional) motor is needed. While many designers of other systems use the unipolar type of motor, we feel it limits the performance of our pump due to the reduced force at even moderate speeds.
Any other questions can be asked of your local  Lee Sales or Applications Engineer.
Glossary
Accuracy
The difference between the intended value and the desired, or specified value. Usually used to relate single-event performance of multiple parts.
Controller
The controller is the circuit that outputs pulse signals for controlling the motor.
Current Down
A controller function which automatically lowers the current to a preset value when the motor is at rest. It serves to reduce the heat generated by the motor while stopped.
Duty Cycle
The ratio of time the motor is on to total cycle time.
Microstepping
An electronic control technique that proportions the current in a step motor's winding to provide additional intermediate positions between the actual mechanical poles. Allows smooth operation and high precision and resolution.
Peripheral Volume
The volume in the pump port head (piston chamber) in excess of the piston volume.
Precision
The repeatability of a component or function. Used to express the total variability of a single component or function over multiple events. Used to describe the consistency of performance, without regard to accuracy.
Pulse
A single, usually 0-5 vdc square shaped pulse given as input signal to the controller.
Pulse Rate
The number of pulses per second sent to the controller, each corresponding to a change of state of the windings, and subsequently a rotational step of the motor.
Ramp Rate
The rate of change of the pulse rate, employed to ease the mechanical acceleration and deceleration.
Resonance
This is the phenomenon in which stepper motor vibration becomes largest at specific speeds. While practically undetectable in Lee LPV pumps because of the inherent damping by the seal on the piston, a resonance is present at approximately 150 pps.
Step Angle
The step angle is the distance in degrees that the motor rotates at the input of one pulse from the controller.
Volume Resolution
The smallest increment of displaced volume in a given pump, correlating to a single motor step.
References
1. Stepping Motor System Design and Analysis, C. K. Taft, R. G. Gauthier, T. J. Harned, c 1989, University of New Hampshire.
2. Semix MicroMate Driver Catalog, Semix Inc., Fremont, CA
3. Oriental Motor Catalog, Oriental Motor, Torrance, CA
4. Parker Motion and Control Catalog, Parker Compumotor, Rohnert Park, CA |
For more information, please send us your application information via our ASK LEE service. Or contact our application engineers in the USA at 1-800-LEE-PLUG or our representatives around the world.
Copyright 07/2002 by The Lee Company, USA
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