scjones@sdrc.UUCP (Larry Jones) (07/26/89)
What are the standards for on-hook and off-hook voltage? I just got a second line phone line installed and bought a two line phone. On the old line, all is well. On the new line, the in-use LED is always lit, even when the phone is on-hook. Some quick exploration with my meter shows the on-hook voltage of the old line is about 45V, which gradually drops to about 30V, implying that there's a fair amount of capacitance somewhere that's being discharged by the meter. The new line shows an on-hook voltage of about 25V which is rock steady. The phone's LEDs seem to switch somewhere between 30V and 35V, which seem awfully high to me. So, is the line within spec and the phone hosed, or vice versa? ---- Larry Jones UUCP: uunet!sdrc!scjones SDRC scjones@SDRC.UU.NET 2000 Eastman Dr. BIX: ltl Milford, OH 45150-2789 AT&T: (513) 576-2070 "You can't get a body like mine in a bottle -- unless you push REAL HARD." - Judy Tenuta / Dr. Pepper
rusty@cadnetix.COM (Rusty Carruth) (07/29/89)
In article <767@sdrc.UUCP> scjones@sdrc.UUCP (Larry Jones) writes: >What are the standards for on-hook and off-hook voltage? > >I just got a second line phone line installed and bought a two >line phone. On the old line, all is well. On the new line, the >in-use LED is always lit, even when the phone is on-hook. Some >quick exploration with my meter shows the on-hook voltage of the >old line is about 45V, which gradually drops to about 30V, >implying that there's a fair amount of capacitance somewhere >that's being discharged by the meter. The new line shows an >on-hook voltage of about 25V which is rock steady. The phone's >LEDs seem to switch somewhere between 30V and 35V, which seem >awfully high to me. > >So, is the line within spec and the phone hosed, or vice versa? >---- >Larry Jones UUCP: uunet!sdrc!scjones >Milford, OH 45150-2789 AT&T: (513) 576-2070 "Normal" on-hook voltages are 45 to 50, but the range can actually be 30 and above. Personally, 25 is too low, but I do know that some places use 25 (my parents in Pagosa Springs, for example). Of course, I expect this to raise all sorts of objections :-). It is pretty safe to assume that your off-hook voltage will drop below 10v, if you want to use that as a threshold.... (In case you could not guess, I vote for the phone being 'technically correct', but not designed for 'the real world', and I would say that the phone is 'real world semi-normal', but technically wrong.) Well, here come the corrections! :-) One other comment - 45volt drop to 30 volt over time when you hook up the meter (assuming its more than 1ohm/volt :-) It seems to me that something is unusual in Ohio :-). Technically speaking, the phone line has a 600 ohm impedance... normally, but I understand that can vary from much less to over 1.2k. Anyway, lets assume you are using a 10k ohm/volt meter, and you put it on the 50 volt scale. Ok, then you are placing 500k across the phone line. Quick, whats the current drain? From here, you *could* try to figure out what the effective capacitance is by timing the voltage drop (and assuming that 30v is really the 'minimum voltage' value) and doing some figuring. (You would need to know the 'resistance' of the line, but thats 'easy' - stick a resistor across it and measure the voltage once it stablizes, then use ohms law) Anyway, it seems to me strange that your phone line would gradually drop due to a 500k load. But, then, its been a year or so since I designed anything for the phone system, my memory could be way off. But, thats why I posted - I figure the net will be *sure* to correct any errors I made :-). ---------- Rusty Carruth UUCP:{uunet,boulder}!cadnetix!rusty DOMAIN: rusty@cadnetix.com Daisy/Cadnetix Corp. (303) 444-8075\ 5775 Flatiron Pkwy. \ Boulder, Co 80301 Radio: N7IKQ 'home': P.O.B. 461 \ Lafayette, CO 80026