Member postings for Robert Atkinson 2

No ,

Meant a 24V NVR, powered from the PC terminal and contacts to the safety circuit.

Addressing Bobs comment, while using dual circuit stops is best practice, it depends on the machine. A Failure Modes & Effects Analysis (FMEA) would be carried out and severity of failures addressed. The level of protection will depend on the hazards and use. For a non CNC lathe or mill used by a skilled operator a dual circuit protection system would not normally be required. If you did a safety analysis on a chain saw as a new invention it would never be allowed!.

One particular failure mode of most E-Stops is that the switch module fits on the back of the button assembly and it's actuator has to be pressed to open the contacts and stop the machine. If the switch block is not fitted or falls off for some reason the E-stop wont work, dual circuit or not. The only mitigation for this is testing the E-Stop, but the switch block could drop off as you reset it. I've looked for a fail-safe E-Stop but never found one.

Robert G8RPI.

You could use a 24V no-volt release start / E-Stop module. These a re cheap enough. Arrange the guard switch(es) to drop out the no volt coil and one contact to the VFD.

Robert G8RPI.

OK don't bin it, "dispose of in a legal and environmentally friendly manner" with extreme prejudice

Being PTC based means it will maintain temperature but is no indication of the quality of insulation, It is very difficult / expensive to achive good thermal conductivity and the electrical insulation, including creapage and clearance, required for a class II (double insulated) appliance. I would be VERY suroised if this iron met the required safety standards. it is cheaper to use an earth wire. This was probably designed for 100 /115V

The UK importer probably went of of business so they didn't have to give refunds. Several of the items on the archived webpage clearly would not meet european safety standards e.g. 2 bar electric fire.

Robert G8RPI.

Tell me about it. 6 GPSDOs, (one Rubidium), 4 other Rubidium oscillators, LF off-air standards, GPS receivers, crystal oscillators (some cost thousands of pounds when new) about 10 frequency counters including HP 5370B and Philips PM6654, the list goes on....

Robert G8RPI.

Hi John,
Nice lathe, but unfortunatly the inverter installation is very poor and potentlly dangerous.
1/ No strain relif on the power leads.
2/ One lead  has its ground lead unter tension. If the lead is pulled this could come off. If the motor earth comes off with it it could possibly touch the live terminal next to it and making the motor case live even if not running.
3/ Mounting is wrong. The front panel and thus channels through the heatsink, should be vertical for proper convection cooling.
4/ You appear to be using the front panel controls for normal operation. They are only intended for initial set-up and maintenence.
5/ The drive should be in an enclosure.

1/ & 2/ are the most important and should be addressed. The heatsink is probably common to higher rated models and is probably OK at the power and duty cycle you are running.
As a minimum you should really have an external emergency stop rather than relying on the front panel controls.

If it is a personal item with no one else able to access it then the condition is purely your concern. But you have posted pictures that others may copy so I feel obliged to point out the issues so they do not take it as an acceptable example of VFD installation. Nothing personal.

Robert G8RPI.

Edited By Robert Atkinson 2 on 06/04/2021 18:53:33

The lead is probably stiff because it is cheap and nasty heat resistant cable. The connector is non-standard. This is because you should not be able to use a non heat resistant cable on a heating device ( hence difference between C13 computer leads and C15 kettle leads). Using a different lead by modifying it or the iron will reduce its safety.

A bigger concern is the sole plate of the iron appears to be metallic This would almost certainly need a 3 core earthed connection. I would bin it and by a travel iron from a reptutable manufacturer. While this one does have a CE mark, the label is clearly not compliant and the website does not exist.

Robert G8RPI.

Edited By Robert Atkinson 2 on 06/04/2021 18:21:27

The actual experiment was more about different means of time transfer, fibre optic vs direct ( free space) laser than the actual references themselves. The problem is that it takes time to transfer the time from one place to another. Even in the time of clockwork noon at Greenwich was signalled by both sound and visual signals as sound takes too long to travel. Thransferring time long distances relied on radio but even this has delays. When HP desigined the 5061A "transportable" cesium beam frequency standard in the early sixties the enabled "flying clocks and accurate time transfer around the world.
https://www.hpmemoryproject.org/news/flying_clock/celebration_01.htm

Robert G8RPI.

It was not a quip, the oscillator I was refering to is a quartze one (HP 10811D based) and it has a detectable change in frequency when turned on its side or inverted.

Robert G8RPI.

In my home workshop I can measure time to 20 picoseconds for one off events, much better for something that can be averaged. Thats 2x10^-11 or 0.00000000002 s. Thats good enough for most practical purposes. Light travels about 6mm in 20 ps.I can measure frequency to over to 25 GHz (2.5s10^10). I have 4 atomic frequency standards, but like most time nuts I mostly use GPS based clock. I have several of those with 3 different models running 24/7. You need three because if you only have two and they are different you don't know which is right
I built a precsion quartz oscillator at over the weekend. I can easily see the effect of gravity on this e.g. the frequency change when you turn it on its side, +1 G to 0 G

Robert G8RPI.

The Inspiration steam car holds the record at139.8 mph set in September 2009. Designed by Glynne Bowsher who also designed signifcant parts of Thrust 2 nd Thrust SSC. Bodywork was by Mike Horne also of the two Thrust car teams. Glynnne is a long time steam train enthusiast.

Robert G8RPI.

Almost certainly the pump is overhating causing a thermal trip to cycle and previously stated by Stuart and David. If it's 10 years old just buy a new one.

Robert G8RPI.

Hi Peter,

Your earlier comment sounds correct. The lights are generating interference an you are an antenna bringin it close to the DRO. The mill body is acting as a "ground" return capacitively coupled to the DRO. By touching the mill with one hand you and the mill are at the same voltage and the interference has no effect.

I thought it was the other way around with th milll body being the intererence source and you the ground, bu the end effect is the same. The "metallic" cse version my well sort the problem.

Robert G8RPI.

If not stuck to something ferrous they should be OFF. This 1/ preserves the magnetisim (less important with modern magnets but who knows what is inside a given base), 2/ It stops the base picking up stray bits of swarf etc.

Likewise magnetic chucks should always be off when not in use. A third reason applies to chucks, safety. They are powerfull enough to cause injury if they "grab" a tool or workpiece with your hand between them.

Robert G8RPI

Does it work OK if the mill is turned off at the socket? Fully unplugged at the mains?
I think the problem is interference with the mill bodywork being noisy. Your body is providing a return path.
You could also try firmly grasping the pillar with oe hand while pressing the buttons.

Robert G8RPI.

That inverter is awful.
1/ 220V rated, UK is nominal 230V, typically 240V. This DOES matter especially if design is marginal anyway.
2/ Case looks like cheap polystyrene with heavy heatsink supported by self tappers through the side.
3/ No rear cover, PCB connectons exposed.
4/ Mains input and motor connections have no strain relief and I can't see separators either.
5/ No EMC protection.
6/ Non UK seller so possible customs / support issues.

EMC affects other people, not just you.

Robert G8RPI.

I think Dave is talking about the simple speed controls used on cheap machines from the far east with DC motors. These have little or no protection.

Robert G8RPI.

To add another option, toughened acrylic adhesives such as loctite F246 or 330 work well and are easy to use. You put an activator on one surface and the "glue" on the other. Some manouvering to adjust is possible for several seconds but it set up to holding strength quickly enough to hand hold it. Note the activator may be sold separately.

Blooming forum, Just typed a long erply and lost it.

Short version:

sensor optotransistor ran from same regulated supply as the comparator so not much variation and the signal and set point are ratiometric.

Arming is so circuit can tell the difference between nothing in the opto and the target slot. Basically the sequence is:

A/ Nothing in optocoupler, photo transistor "ON" - not home
B/ Solid part of target enters optocoupler, photo transistor "OFF" Circuit "arms"
C/ Slot in arget aligns with sensitive axis of optocoupler, photo transistor "ON" - in home position.

As a bonus step B is used to switch the speed of the axis during homing to a slower speed allowing faster more accurate homing.

You don't need the arming for a pendulum detector. If you have trouble screening the pendulum from ambient light, a long, curved target that obscures the slot throughout the swing, with slot or hole a trigger point, will help because it will block ambient light as well as the LED.

Robert G8RPI.

They can be even better with some additional electronics and a slotted target. I did some work years ago to look at replacing expensive high precsion home sensors on a instrument in production.
We used a target with slot in the middle. The obscuration as the target entered the slot "armed" the circuit (We used a PIC microcontoller but a dual flip-flop and bit of logic will do) and then the narrow slot gave the actual home position. The coupler LED had constant current drive and the output was fed to a comparator with accurate reference. The sesor was shielded from ambient light. The target was thin laser cut stainless steel to reduce alighnment issues.
We were getting sub-micron repeatability. Measurement was using a Rennishaw ML10 laser interferometer. I could easily measure thermal expanssion of the 100mm long test rig if I moved the reflector from one end to the other.

The most important things are keeping ambient light off the sensor, keepng LED current constant (using just a resistor is not good enough with a 5V supply due to variation in LED Vf with temperature. A resistor is OK with a suply > about 9V) and using a comparator on the sensor output. A logic chip with schmitt trigger input is OK.

Robert G8RPI.

It's easy to check the amount of alcohol in petrol, all you need is a measuring cylinder. Put some petrol in an note the volume. Add at least 1/3 more water, shake well and let it settle. If there is alcohol in the fuel the fuel volume will go down as the alcohol dissolves in the water (water volume will increase). The % volume reduction equals the alcohol content.
High alcohol also makes vapour lock more likely. This can affect early fuel injected cars causing poor starting after a hot soak.

Robert G8RPI.