Maximum demand ammeters

The old school way was a conventional ammeter movement with a pointer that showed the demand in real time, and a second pointer, often red in colour, that was pushed around the scale by the ordinary pointer. The red pointer therefore displayed the highest reading registered.

Sometimes a thermal ammeter was used with a time constant of a minute or two, as this avoided recording peaks due to motor starting etc.

Re-setting was manual by a push button or small knob turned by the fingers.

The readings were recorded in a record book, either every reading, or only unusual readings.

The modern is a digital instrument with electronic memory, probably  downloaded to a PC.

Thanks broadgage I can imagine it's a useful feature  if a sub is suffering from random fuseblowing  or overheating transformer 

Very old ones used a glass tube, curved so that ball bearings inside were stuck in positions connected to a “strong” movement. The balls left in the tube showed how far it had rotated. Clever idea, but now lost in the mists of time.

The actual thing

You got to admire engineers of old some of the ideas of the past are truly amazing

Kelly Marie Angel: 
 

You got to admire engineers of old some of the ideas of the past are truly amazing

What always impresses me is the standard telephone connection. Using only 2 wires and passive electronics it can: supply power; supply a ringing signal; supply audio; send audio; send an indication of on or off hook; send dialling numbers.

True the humble Dog n Bone is very cleverly engineered

wallywombat: 
What always impresses me is the standard telephone connection. Using only 2 wires and passive electronics it can: supply power; supply a ringing signal; supply audio; send audio; send an indication of on or off hook; send dialling numbers.

You forgot broadband!

I think that it was more impressive in the days of switchboards and dials rather than buttons. In college, the telephonists occasionally allowed me to make a call, but only on condition that I sat at the switchboard and did the work myself. What was it: forward for ring, backwards for speak? It was a long time ago.

The downside was that the mechanical phones were less reliable than solid state ones.

wallywombat: 
 

Kelly Marie Angel: 
 

You got to admire engineers of old some of the ideas of the past are truly amazing

What always impresses me is the standard telephone connection. Using only 2 wires and passive electronics it can: supply power; supply a ringing signal; supply audio; send audio; send an indication of on or off hook; send dialling numbers.

Which is why they intend to switch it all off, and replace it with a much more complicated VOIP system, which won't work if there's a power cut.

Which is why they intend to switch it all off, and replace it with a much more complicated VOIP system, which won't work if there's a power cut.

Many will expect to will fall back to a mobile phone, whose base stations are not backed up in the way a traditional exchange is/was, so if that power cut is wide-area you may find that all non private comms and internet is lost after an hour or two. For a power cut that is occasional, maybe that is OK, depends rather where you live and your state of health.

Ever thought of taking the exam for amateur radio? It is surprising how far a rig running off a car battery can get out.

Mike.

G7VZY