1. A method of driving current from an AC power supply through a series arrangement of a varying number of strings of LEDs, the method comprising,
adding LED strings to the series arrangement in a first order during an increasing voltage part of a cycle of the AC power supply cycle and subsequently
removing LED strings from the series arrangement in a second order s during a decreasing voltage part of the cycle,
wherein the second order is not the reverse of the first order,
2. The method of claim I wherein the second order is the same as the first order.
3. The method of claim 1, comprising switching a short-circuit across a string of LEDs to remove that string of LEDs.
4. The method of claim 1, comprising switching between two current sources to add a string of LEDs.
5. A driver for driving, current from an AC power supply through a series arrangement of a varying number of strings of LEDs by adding LED strings to the series arrangement during an increasing voltage pan of a cycle of an AC power supply cycle and subsequently removing LED strings from the series arrangement strings of LEDs during a decreasing voltage part of the cycle,
the driver comprising
at least: one short-circuit connection configured to be switchably connected across a one of the strings of LEDs, and
at least: one current source configured to he connected to the series arrangement,
and being configured to add the LED strings in a first order and remove LED strings in a second order which is not the reverse of the first order.
6. A driver as claimed in claim 5, wherein the second order is the same as the first order.
7. A driver as claimed, in claim 5, configured to switch short-circuit connection across a string of LEDs to remove that string of LEDs.
8. A driver as claimed in claim 5, configured to switch between two current sources adds a string of LEDs.
9. An integrated circuit comprising a driver as claimed in claim 5.
10. A driver for driving current from an AC power supply through a series arrangement of a varying number of strings of LEDs, the number of strings of LEDs being varied by adding LED strings to the series arrangement in a first order and subsequently removing LED strings from the series arrangement in a second order, the driver comprising
a plurality of switches each configured to short-circuit at least one of the stings of LEDs.
11. A driver configured to operate a method according to claim 1.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A measurement scale tensioning device suitable for tensioning a scale readable by a readhead while the scale is mounted to a substrate, the device comprising;
a preloadable member operable to urge the scale into tension while the scale is mounted to the substrate.
2. The measurement scale tensioning device of claim 1, further comprising a securement that secures each end of the scale to the substrate, and a further securement that secures the device to the substrate while the device is in operation.
3. The measurement scale tensioning device of claim 1, wherein the preloadable member includes a resilient part, and the tensioner includes a loading part that preloades the member and that releases a preload.
4. The measurement scale tensioning device of claim 3, wherein the loading part includes an eccentric, rotatable to effect the preloading and release of the preload.
5. A method for tensioning a measurement scale comprising the steps of:
providing a measurement scale and a scale tensioner;
mounting the scale to a substrate;
securing one end of the scale to the substrate;
preloading the scale tensioner;
securing the tensioner to the substrate adjacent another end of the scale;
releasing the preload in the tensioner to cause a tension in the scale;
securing the other end of the scale to the substrate while maintaining the tension in the scale; and
releasing the securement of the tensioner.
6. The method of claim 5, further comprising the steps of;
preloading the scale tensioner again;
re-securing the tensioner to the substrate adjacent the other end of the scale;
releasing the preload in the tensioner;
releasing the securement of the scale at the said other end, thereby allowing further tension in the scale;
re-securing the said other end of the scale to the substrate, whilst maintaining the further tension in the scale;
releasing the securement of the tensioner; and
repeating the aforementioned steps until the scale extends substantially no more on application of the further tension.
7. The method of claim 5, further comprising the step of removing the tensioner from the substrate following securement of the scale at the other end of the scale.
8. The method of claim 6, further comprising the step of removing the tensioner from the substrate following re-securement of the scale at the other end of the scale.
9. The method of claim 5, wherein the step of securing the scale to the substrate includes the provision of a track to hold the scale to the substrate.