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Telephone CO Question
Telephone CO Question...
If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
Telephone CO Question
On 4/15/2011 7:48 PM, Jim Thompson wrote:
Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson See if this will help, Jim. http://www.affordablephones.net/phoneline.htm John |
Telephone CO Question
On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson
wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie |
Telephone CO Question
On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E.
wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed |
Telephone CO Question
On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E.
wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed |
Telephone CO Question
On Fri, 15 Apr 2011 18:34:32 -0700, Jim Thompson
wrote: On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E. wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson How far are you from the CO ? Don't forget to add the miles of copper resistance of the loop. boB |
Telephone CO Question
Jim Thompson wrote:
I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). Try values of R between 0 and infinity. I did once and calculated my line source resistance, but I forgot what it was. -- Reply in group, but if emailing add one more zero, and remove the last word. |
Telephone CO Question
On 16 Apr 2011 03:06:02 -0500, boB wrote:
On Fri, 15 Apr 2011 18:34:32 -0700, Jim Thompson wrote: On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E. wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson How far are you from the CO ? Don't forget to add the miles of copper resistance of the loop. boB Across the park from the CO... maybe 1/2 mile as the wire goes ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed |
Telephone CO Question
On Sat, 16 Apr 2011 04:10:57 -0400, "Tom Del Rosso"
wrote: Jim Thompson wrote: I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). Try values of R between 0 and infinity. I did once and calculated my line source resistance, but I forgot what it was. Good point. I just did open and short measurements. A variable R would detect if it's resistive or an active circuit (like a current limiter). ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed |
Telephone CO Question
On 16 Apr 2011 03:06:02 -0500, boB wrote:
On Fri, 15 Apr 2011 18:34:32 -0700, Jim Thompson wrote: On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E. wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson How far are you from the CO ? Don't forget to add the miles of copper resistance of the loop. boB And all the inductance/capacitance of that loop cable! But I wouldn't worry too much, as it is pretty benign. However, consider lightning surges from nearby strikes! Charlie |
Telephone CO Question
On Sat, 16 Apr 2011 08:49:53 -0700, Charlie E.
wrote: On 16 Apr 2011 03:06:02 -0500, boB wrote: On Fri, 15 Apr 2011 18:34:32 -0700, Jim Thompson wrote: On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E. wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson How far are you from the CO ? Don't forget to add the miles of copper resistance of the loop. boB And all the inductance/capacitance of that loop cable! But I wouldn't worry too much, as it is pretty benign. However, consider lightning surges from nearby strikes! Charlie All underground here. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed |
Telephone CO Question
On Sat, 16 Apr 2011 08:49:53 -0700, Charlie E.
wrote: [snip] And all the inductance/capacitance of that loop cable! But I wouldn't worry too much, as it is pretty benign. However, consider lightning surges from nearby strikes! Charlie What sort of "pop filter" could be placed across the line without upsetting Ma Bell? 4.3K in series with 10nF ?? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Remember: Once you go over the hill, you pick up speed |
Telephone CO Question
On Sat, 16 Apr 2011 08:52:33 -0700, Jim Thompson
wrote: On Sat, 16 Apr 2011 08:49:53 -0700, Charlie E. wrote: On 16 Apr 2011 03:06:02 -0500, boB wrote: On Fri, 15 Apr 2011 18:34:32 -0700, Jim Thompson wrote: On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E. wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson How far are you from the CO ? Don't forget to add the miles of copper resistance of the loop. boB And all the inductance/capacitance of that loop cable! But I wouldn't worry too much, as it is pretty benign. However, consider lightning surges from nearby strikes! Charlie All underground here. ...Jim Thompson Can still couple to the cable, as the strike goes to ground... Charlie |
Telephone CO Question
Jim Thompson wrote:
On Sat, 16 Apr 2011 08:49:53 -0700, Charlie E. wrote: On 16 Apr 2011 03:06:02 -0500, boB wrote: On Fri, 15 Apr 2011 18:34:32 -0700, Jim Thompson wrote: On Fri, 15 Apr 2011 17:57:27 -0700, Charlie E. wrote: On Fri, 15 Apr 2011 17:48:07 -0700, Jim Thompson wrote: Telephone CO Question... If I suddenly load a short on a telephone line (initial conditions on-hook)... what is the PEAK current flow that could occur? Is it the same as the "loop current"? How is limiting done in a modern CO, series R, or an active circuit? Thanks! ...Jim Thompson \ Hi jim, I don't know what they do today, but in the olden days there was a coil that was activated by that current, so was limited by the coil (and line) resistance. In modern CO equipment, they would basically have a active sense circuit to detect and measure that current. Too little current, and they determine a line fault condition. Probably too much causes an alert as well. Since there are multiple customer circuits on a single line card, I would assume that they basically have a resistor in there to measure current across, and maybe a relay to cut the line power if it is out of service... Charlie I have sort of a weird line... almost textbook... 50VDC open circuit, 50mA DC when shorted, so a 1K source impedance (or an active circuit). I going to switch on a "noise maker"... at first jolt, it's simply just a small valued resistor in series with a zener and a diode. I don't have any current probes so I was just trying to estimate the initial surge. I guess just try it while keeping my face covered ?:-) ...Jim Thompson How far are you from the CO ? Don't forget to add the miles of copper resistance of the loop. boB And all the inductance/capacitance of that loop cable! But I wouldn't worry too much, as it is pretty benign. However, consider lightning surges from nearby strikes! Charlie All underground here. ...Jim Thompson Famous last words. Lightning can (and seems to prefer) striking high value underground equipment to some depth. And then there are plain old power system faults that cause nearby, mutually grounded conductors (cables in the same trench) to jump in voltage. Invest in a couple of surge arresters (even spark gaps are better then nothing). -- Paul Hovnanian ------------------------------------------------------------------ "Nothing Important Happened Today" -- King George III, diary entry July 4, 1776 |
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