[GreenKeys] Can anyone identify this machine

[Martin]

Thanks for this information.

I will resume the problems with the ST5000 shortly and I will let you 
know how I get on, but meanwhile other issues are pressing!

Best wishes

Martin

On 02/03/2018 17:57, Ralph Mowery wrote:

> For a 160 volt supply you need a total resistance of 8000 ohms in the loop.  That is calculated at 160 volts divided by the .02 ma you want for the loop.   The coils for the machine are usually around 50 to 200 ohms depending on the machine and if they are in series or parallel.  The st5 probably has a resistor of around 2000 to 2500 ohms that can be adjusted for the 60 ma needed.
>
> I think if I wanted to use it on a 20 ma loop then I would get a resistor of 7500 or 10000 ohms and 10 watts that had a slider on it to adjust to 20 ma. Make sure you turn off the st5 before adjusting the slider and give the capacitors time to discharge. If I had some fixed resistors of 10 watts or more,I would put about 6000 or 7000 ohms in  series with the loop and adjust the on inside the st5 to give the 20 ma that you need.
>
> If you are not up on the loop theory, here is a very short and simple theory.
>
> The coils of the teletype machine take less than 20 volts to make them pull in.
> However due to the inductance of the coils it takes some time for the current to go from 0 to 20 ma.  This is sort of like a car.  If you want to get to 50 MPH  or think you are on the metric, 80 KPH low horse power will get you there, but it takes a while . Higher horse power will get you there faster.  AS you only have about 20 milliseconds, you need to get there fast.  That is why a loop needs to be around 100 or more volts and a resistor is set to limit the maximum current. It also helps burn the oil and other dirt off the contacts of the keyboard.
>
>
> -----Original Message-----
> From: Martin [mailto:strowger at aeolian-hall.myzen.co.uk]
> Sent: Friday, March 02, 2018 10:59 AM
> To: Ralph Mowery
> Subject: Re: [GreenKeys] Can anyone identify this machine
>
> I was wondering about that.
>
> Its 160 volts.
>
> Martin
>
> On 02/03/2018 15:36, Ralph Mowery wrote:
>
>> Without knowing the exact voltage the st5000 puts out it is hard to calculate the exact value, but if you put a resistor of around 7000 ohms and probably around 5 or 10 watts  in series with the loop you would have your 20 ma current loop.
>
>

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