Frequently asked questions

Pre-sales questions

What method of sealing is the piston to cylinder interface?
Where can we source spare cylinder seals, should they become necessary?
What is the maximum pressure differential between the two sides of the piston?
What is the maximum operational pressure of the machine?
What is the range of flows/tidal volumes?
What LabVIEW software versions are available?
Is the source code available?
What sort of warranty is supplied with the machines?
How would delivery be achieved?
What is the likely delivery schedule?
What size air fittings are supplied?

Set-up questions

What is the correct data acquisition card configuration?
Is there a longer interface cable available?
Details of the USB connection
Registry errors at setup

Support questions

One of the Red LEDs on the actuator is not lit and the piston won't move
What are the error codes shown on the LED on the controller unit?
The piston moves then stops each stroke - resulting in an incomplete wave being produced
The piston is becoming very noisy when moving
Flow is not as expected
Piston jumping - not moving smoothly
Opening the machine

Flow measurement unit

What are the connections to the breathing measurement unit and how does it work?

Pre sales questions

What method of sealing is the piston to cylinder interface?
Sealing of the piston around the cylinder wall is achieved in the earlier machines by the use of a labyrinth seal. This means that there is no wear component in the system, but equally means that there can be cross contamination between the two sides of the piston and a pressure differential across it cannot be maintained.
Later versions of the machine (post July 2009) use a wiper seal at the periphery of the piston to remove these limitations but this does introduce a wear component that may need replacing very occasionally (depending upon the usage of the machine).

Where can we source spare cylinder seals, should they become necessary?
Spare cylinder seals are available directly from Warwick Technology Limited.

What is the maximum pressure differential between the two sides of the piston?
The machine is designed to operate with the two sides of the piston almost pressure balanced. The pressure top and bottom can vary by approximately breathing pressure differentials - i.e. up to 200mBar.

What is the maximum operational pressure of the machine?
The basic machine has been built to operate at atmospheric pressures. However, a version is currently being developed for use with hyperbaric breathing chambers, operating at up to 61 bar (proof pressure 100 bar). Other requirements can be designed and constructed as required.

What is the range of flows/tidal volumes?
As the system is electronically controlled, the flow rates and/or tidal volumes are infinitely variable up to the maximums quoted. See elsewhere on this website for the standard machines properties. At the very low flow rates/tidal volumes (>2%max) the machines may be less accurate in generating the waveform as the piston will not be moving a great deal and compressibility becomes more of a factor. Machines with different (small or larger) limitations can be easily developed to order.

What LabVIEW software versions are available?
The LabVIEW software provided with the machines is currently to LabVIEW version 7.1. Versions back to LabVIEW 6.0i can be provided by request. Later versions of LabVIEW will automatically convert older versions when loaded.

Is the source code available?
The machines are provided with the full code versions of the LabVIEW VIs i.e. with the source code attached. This enables users to develop or customise the software further if required. The code is provided locked against accidental modification but not password protected.

What sort of warranty is supplied with the machines?
The machines are warranted against defects in material or manufacture for a period of one year from date of delivery. Repair and service will be undertaken by either Warwick Technology ourselves or directly by the major component suppliers.

How would delivery be achieved?
Delivery within the UK will usually be undertaken personally by Warwick Technology Limited. Delivery to clients abroad is undertaken using air freight shipping. The machine is supplied in one wooden crate (415x415x700mm - 75kg) containing the machine itself and all it's associated equipment.

What is the likely delivery schedule?
All machines are built to order and manufacture is normally expected to take 10-12 weeks from receipt of order. Non-standard machines may take a couple of weeks longer. Air freight shipping to overseas customer can add 7-10days. Contact us for more information.

What size air fittings are supplied?
As standard the machine is fitted with two 1"BSP stainless steel hose tails on elbows, one screwed into each of the top and bottom plates. Different configurations of fittings and locations are available as required.

Set-up questions

What is the correct data acquisition card configuration?
The supplied NI-6024E DAQ data acquisition card needs to be configured correctly to enable the machine to operate correctly. The card needs to be set up as follows:
  • Analogue inputs - Referenced Single Ended (RSE) configuration
  • Analogue Outputs - 10vdc output range (bipolar)
The card configuration can be accessed and altered using the Measurement and Automation Explorer (MAX) installed with the DAQ card drivers. Refer to the National Instruments manual for details..

Is there a longer interface cable available?
A longer interface cable is available direct from us for an additional charge (1 metre cable from PC to machine is supplied as standard). However, the cable is a standard straight through 50 way IDC cable. The use of cables with lengths of up to 5m appear to be have no discernible impact on the system.

Details on the USB connection
The latest version of the Breathing Machine are supplied with a built-in USB interface. This only requires a spare USB port on the controlling computer. This removes the need to open the controlling computer and fit a PCI card, plus the configuration is simplified as the configuration is handled by the driver software itself.

Registry errors at setup
The system needs to create a series of registry keys to store setup information. The installation will attempt to create these keys at startup. If the user does not have privileges on the systemn to do this an error will occur either during installation or the first time the software is run. Log in with admin rights to allow the keys to be created. This may cause issues with later versions of windows

Support questions

One of the Red LEDs on the actuator is not lit and the piston won't move
These red LEDs show the status of the limit switches protecting the actuator. Over extension will result in the lower LED going out. Over-retraction will result in the upper LED being extinguished. If either LED is not on the piston is held stationary for safety. If the top LED is not on as the cycle should start it can occur due to a slight drift of the hall effect position. A solution is to loosen the switch mount and very gently and very slightly move the switch upwards. No more than a fraction of a millimetre movement should be required to illuminate the switch again.
The lower LED should never be extinguished as the software should not allow a breathing pattern incompatible with the available range of movement to be created.
In either event the first approach should be to try to reset the machine using the Machine Reset program. This will disable and then re-enable the machine and try to move the piston to its park position. If the piston has only moved just into it's protected area it should be able to move back into the safe zone and operate as normal again. If trying this a few times still fails then contact Warwick Technology for assistance.

What are the error codes shown on the LED on the controller unit?
Between the two sets of terminals on the top of the controller unit is green LED. When the machine is powered and ready to run or during normal operation, this LED will pulse rapidly (24Hz). This will flash at a slow rate if a controller error occurs, with the number of flashes indicating the error. Refer to the controller manual supplied on the driver CD for more information on these codes. However, the most common error shown here is positioning error (four flashes) implying the piston has been commanded to go to a position it cannot move to fast enough. This should not occur in normal operation. Again try the system reset program a few times. If this does cure the problem and return the machine to operation then please contact us.

The piston moves then stops each stroke - resulting in an incomplete wave being produced
This error has been noted on a system in which the data acquisition card had been incorrectly configured to only provide a 5volt output. The signal to the breathing machine relies on 0-10vdc being 0-100% of actuator travel. Confirm the card configuration as detailed above and try again. If the problem persists then fell free to contact us.

The piston is becoming very noisy when moving
The piston on the older machines uses only a labyrinth seal whereby the piston is very closely toleranced to the cylinder wall (with a gap of about 2 thousands of an inch). This will always be slightly noisy though it is possible to lubricate the interface as long as this will not interfere with the operation of whatever test is being performed.
One option that is often used is to spray the inside of the cylinder with PTFE dry lubricant. Contact us for details on how to open the machine and for a source for this spray. New machines should not suffer with this problem as they use a PTFE seal at the piston edge.

Flow is not as expected
The figures quoted for flow from the machine are determined by the hardware of the machine itself. The piston movement is constantly fed back to the controller unit to ensure correct positioning. Failure to drive the piston to the commanded position will be discernible as an error will be shown on the controller. Therefore differences from the expected flow should not occur. Check the system for leakage and the DAQ card configuration (if used) for the error described above. Contact us if this continues to be an issue.

Piston jumping - not moving smoothly
This can sometimes be caused by overloading of the processor preventing it from driving the controller smoothly. This is unlikely as the software provided is not processor intensive. With an older design machine it may be the piston has become worn and is sticking internally, requiring lubrication. Aerosol PTFE spray can be applied to the inside of the machine cylinder, assuming this will not interfere with the test protocol. Newer design machines with edge seals already use a PTFE seal so do not require this and are less likely to stick or become noisy in this way. Another possible issue is degradation of the feedback potentiometer in the actuator itself. If this is suspected please contact us to arrange servicing of the actuator.

Opening the machine
Should you need to open the machine then it is important to contact us for detailed instructions. Opening or dismantling the machine should only be attempted under our instructions. Failure to abide by this request may invalidate the warranty.

Flow measurement unit

What are the connections to the breathing measurement unit and how does it work?
The breathing measurement unit consists of a flow head, within which the air passes through a gauze, and a digital manometer, which measures to pressure drop across the gauze created by the airflow, and converts this to a flow rate. The flow rate value is provided as a voltage at the connection at the back of the unit and a lead is provided to plug into the interface box on the machine. The voltage conversion on the standard measurement unit is 5vdc for 1000LPM. It does not matter which way around the two pressure pipes are connected to flow head. Reversing them just reverses the positive measurement direction of the flow .











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