Anyone here know the Australian standards for
a) DC voltage on a quiescent telephone line. b) voltage (peak and RMS) and frequency of ring current . Is it a pure sine wave? c) are the standards maintained throughout the Aus system, regardless of the exchange type and manufacture, eg Ericcson AXE etc.?
Many thanks. I have Googled for hours without sucess. There must be an Australian standard somewhere!
it's an elv system so 48vdc is usual and about double on a ring o you could just drag the scope out and look
Hi, as far as I'm aware there is no standard for the PSTN itself as an entity only standards for the equipment connected together and the cabling.
in the old days I'd refer you to TPH1292/1053 which indicates ring signal to be: Voltage: open cct EMF of 75-100V. rms Nominal freq : 17-50Hz Source impedance:500-2000 ohm Periodicity: 0.4s on, 0.2s off, 0.4s on 2s off. minimum length of ring 0.5s.
A call indicating device shall operate satisfactorily on a minimum of 4mA of
17Hz ring signal, 5mA of 25Hz ring signal and 6mA of 50Hz ring signal.The DC voltage from public exchanges and PABXs is nominally -50V wrt earth within the limits of -44V to -56V.
but as that standard is well and truly obsolete try one of those below.
Chers Greg
--------------------- Standard Telephones: AS/NZS60950, AS/ACIFS002, AS/ACIFS004, AS/ACIFS040
Customer Switching Systems: AS/NZS60950, AS/ACIFS002, AS/ACIFS003, AS/ACIFS004
Analog Terminal/Telephone Adaptor (ATA): AS/NZS60950, AS/ACIFS002 (FXO) AS/ACIFS003 (FXS)
AS/CA S003:2010 Requirements for Customer Access Equipment for connection to a Telecommunications Network
AS/ACIF S004:2008 Voice frequency performance requirements for Customer Equipment
AS/ACIF S008:2006 Requirements for customer cabling products
AS/ACIF S040:2001 Requirements for general use Customer Equipment for use with the Standard Telephone Service- Features for special needs of persons with disabilities
AS/ACIF S041:2009 Requirements for DSL Customer Equipment for connection to the Public Switched Telephone Network ANSI Standards
ANSI/TIA-968-A-2002 Telephone Terminal Equipment Technical Requirements for Connection of Terminal Equipment to the Telephone Network
T1.601:1998 ISDN Basic Access Interface for Use on Metallic Loops for Application at the Network Side of NT, Layer 1 Specification IEC Standard
IEC 60603-7 Ed 3.0 (2008-07) Connectors for electronic equipment - Part 7: Detail specification for 8-way, unshielded, free and fixed connectors
on 9/10/2010, StrandElectric supposed :
I think you will find all the Telstra system is the same and described in another post.
There are all sorts of differences in PABXs from various manufacturers and although I cannot define them, lots of PABXs will not work with a TELSTRA hand set.
For instance FAXes will not work on many PABXs so a dedicated line is required in an office needing a fax, not just an extension on the office PABX.
What's the situation regarding grounding of one side of the line, as you would with a scope not using isolated or differential inputs?
Dunno I have to trouble with my portable dicksmith cheapy and believe me it's a cheapy
Thank you Greg. Very comprehensive and just what I wanted.
Ring is some AC voltage (60V?) at 16-2/3Hz superimposed on the -48V off-hook signal.
Some PABXs and similar devices use a trapezoidal waveform instead linksys VOIP adaptors produce a fairly good approximation of a sine wave IIRC. the ring frequency may differ with these too.
Don't, or atleast don't get caught, it may show up as a fault at the exchange.
Best use differential inputs.
52.8 v.
130 v.
Set by ACMA.
Thanks for that, but I've since got the info that the normal nominal line voltage is 48 volts DC and the ring current is RMS 90 volts at 16.6 Hz, so I guess your figures must be the maximum allowed?
The 90VAC ring superimposed on the 50VDC line gets you about 140V or so during ringing with whatever voltage the line drops.
which is why on a hot day it zaps ya on a ring when stripping stuff
I should explain that I worked for Telstra for 23 years as an analog exchange technician. For those exchanges the battery backup consisted of the batteries being 'floated' across the power supply. The batteries were 24 x 2 volt hence a nominal 48 volts, but the power supply was set at 52.8 to maintain the battery charge. The ring voltage is/was 80 volts AC which when added to the 50 volts gives 130 volts peak. Its enough to give a non lethal shock.
Actually, I don't think superimposing AC on DC produces such a simple result... Tyically, a bell is connected via a capacitor so would not even see a DC voltage. Therefore, offset would not enter the picture
Anyone who has felt the effects of ring current will strongly disagree...
It's peak voltage which bites humans, zaps insulation, etc, etc,
................ Zim
my figure quoted above are my memory of what I've neasured on a working phone line his figure are probably more acurate.
yeah the DC helps the AC half the time and hinders it half the time.
But the gain in the help half is worth more than the loss in the hinder halkf.
when computing power you can ad DC and AC RMS voltages for computing power in a pure resistance
50VDC + 90V RMS AC will deliver the same power into a resistive load as 140V DC or 140V RMS AC.
you forgot bloody hurts through sweaty skin
We are talking about LINE voltage here....not voltage through a capacitor and through a set of bell windings or any other putative components.
Its enough to give a decent boot.
Back EMF will do that too.
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