Radiography - pre-electronic vs. computer-controlled

An electro-mechanical X-ray kit

This is the late 1960's (?) "Pantak Windsor" X-ray machine I used at TWI-N.

The console...

The X-ray head and power-unit behind...

Pre-electronic X-ray compared to computer-control X-ray kit

With computer-controlled X-ray equipment

Key-in the desired Voltage (kV), current (mA) and duration of shot in seconds or minutes and seconds
The computer will check the values are allowable and alert if they are "out of range" for the equipment - it will not act on such inputs
The computer will also assert if a "warm-up" is needed - such as when significantly increasing the Voltage
To take the X-ray shot you simply press the green button and everything is done for you

With this pre-electronics equipment

Voltage (kV) and Current (mA) are controlled by the two rotary control knobs. They don't have a scale and you have to watch the meters on the console as you turn the control-knobs. Then action of each control is not independent. If you change just the voltage setting the current is affected. Same for the current control - the voltage is affected. So you have to turn both knobs simultaneously, watching both kV and mA.
You have to set-up the current and voltage for the next shot before you set-up your component and film under the X-ray head. Because there is no scale for kV and mA - there cannot be, as they float around in a complex relationship - you have to set the machine running and adjust the voltage and current controls until you reach the desired values. You can then stop the machine on the red button and go set up your shot.
(you cannot have your next X-ray film in place during voltage / current setup! - it would be getting exposure from the X-rays!!!)
There is a timer with an analogue dial for length of shot. You can switch it between dial-means-seconds and dial-means-minutes. But there is a red outer scale for seconds and a black inner scale for minutes.
When you have set up your shot, when you press the green button for go, the machine should ramp up to the voltage and current settings you obtained in set-up. But there can be a slight drift and you often have to fine-tune the kV and mA (it would be a rare chance that in adjusting one to correctness the other also became correct!). The "drift" tends to be greater the longer the time from set-up to running a shot.
You have to know the warm-up procedure and do it manually. This is to limit thermal shock to the tube and to "burn" contaminant gases out of the cathode to anode path area. You do the warm-up on broad focus (size of the target spot on the anode - yes another manual control!)

On the other hand, this machine has a far wider range of tube voltage down to very low voltages - it will run stable at 25kV - whereas I have met computer-controlled machines which will not go below 70kV. 70kV is above the maximum allowable X-ray tube voltage by specs such as BSEN1435 for many Aluminium components. Let alone the desired voltage for maximum resolution! The power of 6mA on fine-focus of 1.5mmx1.5mm target area is quite good.

So overall, you have to know and nurture the machine, but it gives lovely results.

Another thing - there's also sorts of "clunks", "whirrs", "clicks" and "tickings" of various loudnesses as this machine operates - whereas computer-controlled do not entertain with any sounds at all apart from the intended alerting bleeps.

R D Smith, 18 July 2010