The LT7 series of leak testers have many advanced features:

The leak tester design is highly flexible with respect to software, electronics, pneumatics and mechanics. This allows a wide range of options to be added at any time, even after installation.

To use the graph above, select the size of part from the table on the right. Look along the line of that colour. Select the Parts per minute required from the scale at the bottom and read off the hole size detectable from the scale on the left.

The graph has been calculated assuming a particular conveyor speed of 25cm/s, and sensible bottle diameters for the various sizes. The actual performance of the leak tester could therefore vary from that above.

For information as to the location of items mentioned below, see System Layout and Control Cabinet Internal Layout sections.

Ensure that the leak tester is mechanically adjusted so that the neck of the part is positioned centrally under the test head during the test.

Adjust the Test Head pressure regulator PR10 so that the test head comes down with enough force to seal on the part.

These are the “factory set” values and are intended as a starting point. They can be quickly reached by pressing the “RESET VALUE” buttons together as each setting is displayed.

Send some parts through the leak tester and make any adjustments to the guides that are required.

Adjust the Head Delay so that the part has time to stabilize before the test head descends.

Adjust the Gap Set Delay to achieve a consistent gap between the part just tested, and the next part coming into the test station.

Adjust the Pressurization restrictor RS9 to achieve approximately the required pressurization level (about 3/4 of the way up the pressure scale).

Note the Decay % level obtained for good parts (press the SELECT buttons to display this parameter).

Set the Maximum Decay to a level slightly above this. About 2% above this is usually correct, but this will depend on the consistency of the results. For example, if good parts are coming through with 8.0 % pressure decay on average, set the Maximum Decay to 10.0 %. If the result is always between 7.5 % and 8.5%, the limit can be reduced to 9.0 % to improve the accuracy.

This machine is now fitted with automatically adjusting photoswitches as standard, for part detection. These are advanced background suppression types. They are not confused by container color, transparency, or objects on the far side of the part under test, such as guide rails, people etc. They also project a visible spot of light so that the exact point of detection can be established.

Because the sensors ignore the part color or material, they should rarely need adjustment. However, for completeness the procedure is detailed below.

The sensors have push button adjustment as follows:

If possible, ensure nothing else is in view of the photoswitch (guide rail, guards etc). However, if these are going to be present during normal operation, they should be present during this procedure too.

Press the button on the photoswitch for about 5 seconds until the built in indicator starts flashing.

Hold a part in front of the photoswitch at the position required for detection.

Press the button again (sets turn on level).

Remove the part.

Press the button again (sets turn off level).

Wait until it stops flashing.

This will ensure that the photoswitch only sees objects that are on the conveyor.

The system is provided with a single line alphanumeric display to show all test parameters, diagnostics and results. Push button controls are provided to allow a technician to view items and alter settings where required.

To view a particular item, press SELECT UP or SELECT DOWN until the required item is displayed.

To adjust an item, where appropriate, press the ALTER up and down buttons as required.

To reset a setting to a default value or zero a count, press both of the alter buttons together.

A pressure scale is displayed, in bar graph form. This gives a quick visual indication of the actual pressure in the part at any instant in time. The display is scaled to the set test pressure, so that full scale always equals the set test pressure.

Immediately below the bargraph are indicator lights, which show the results of the test.

The part has passed all tests.

The part has failed a test.

A sensor can be fitted in the test head, which detects blocked or partially blocked neck bores in the part. This light will come on when this is detected. Occasionally other fault sensors may be indicated by this light, e.g. handle flash detection.

This indicates detection of some other fault, which is not a simple leakage. These possibilities are as follows

If the part becomes over pressurized during the test, the pressure may go outside the range of the transducer resulting in an invalid test. This is detected automatically and the part rejected as a precaution. If this occurs, reduce the flow during pressurization by turning RS9 clockwise.

Special test functions or alarm conditions requested by the customer may be indicated using this light also.

The drawings following show the layout and interconnections of the various components, electrically, pneumatically and mechanically. The component numbering system is not obvious and requires explanation.

The heart of the machine is an electronic control system with various inputs and outputs (I/O’s). There are a fixed number of these for any given installation (although extra I/O’s can be added). These I/O’s are connected to various devices (photoswitches, valves, cylinders motors etc), which make the machine work. A controller program reads the inputs and controls the outputs according to its program.

The controller card I/Os have a fixed numbering system, with inputs starting at 0000, 0001, 0002 etc and outputs starting at 0500,0501,0502 etc. The I/O’s are labelled in this way on the circuit card leds, also on the I/O page of the machine display.

The function of a particular I/O number may be different depending on the configuration of machine supplied. There are so many options and configurations that it would be very wasteful to dedicate an I/O for the same function on all machines. Instead, the controller program for a particular machine configuration allocates I/O’s, more or less sequentially.

To avoid having to make individual electrical, pneumatic and layout drawings for each machine combination, Universal Function Numbers have been defined. I/O numbers are related to Function Numbers by a single table in the product manual. Function specific parts (e.g. the Test Head Cylinder) are given a number according to that function (in this case, Cylinder 10). This will be the same in any product that has a Test Head Cylinder; it will always be Cylinder 10, CYL10 etc. The photoswitch that actuates the test head could also be called Photoswitch 10, PS10, etc. The actual I/O number can vary between machine types (although will be the same for two machines of the same model)

The above scheme allows quick on site modifications to a machine to be easily documented and incorporated into the manual, without having to alter all the drawings.

To identify the function of an I/O number, e.g. Output 0500, look it up in the following table. To identify a device labelled by a function number, e.g. Valve 1, look up that number in the Function Numbers table.

This variant is designed for handling larger containers. The main differences from the standard model are:

6mm valve ports instead of 4mm.

Extended setting ranges for long test times.

Higher test pressure range (up to 7 PSI). The transducer is changed to a 15-PSI type and the PCB is a special version calibrated for the new test pressure range.

Option for venting of part before test head released.

External test head valve. The usual internal valve is used to pilot a very high flow external valve. The internal valve must run at system pressure so regulator PR10 is omitted.

RS9 is omitted since maximum pressurisation flow is desired.

Switched 110V output for external conveyor stop/start. This is used to drive an external 3-phase contactor, which switches the conveyor motor.

Reject is by cylinder instead of air jet.

Special program type LT7-C-S1 required.

Because this model of leak tester is expected to be used with unusual parts for test, extra settings have been introduced to allow precise adjustment of every aspect of the test cycle.

Test Time Length of time for leak test. Set to highest value possible consistent with maintaining the required throughput.

Stop Delay Delay between the start photoswitch seeing the part, and conveyor stop.

Head Delay Delay between conveyor stop and test head down.

Fill Time Time allowed for pressurisation. The leak tester will inject air into the part until the test pressure is reached, or until this time elapses.

Start Delay Time between test head up and conveyor start.

Reject Delay Time between reject photoswitch blocked and reject cylinder on.

Reject Time Time for which reject cylinder is on.