 Meter
No. 47A (Ashdown) is a small, line powered table top Subscribers Private Meter (SPM). The
meter detects meter pulses on the line and displays them on two separate
electro/mechanical operated numerical indicators as follows:
- A cumulative total of the number of units used since installation of the meter up to a
total of 99,999 units. Once installed this cannot be reset.
- A display of the number of units used in any one call, or series of calls up to a total
of 999 units. A RESET button is provided and the three digit display can be reset to zero.
To calculate the cost of a call, multiply the number of units used by the charge for one
call unit.
Ashdown can be fitted on either a direct exchange line or an extension of through fed
PBX's / Call Connect system. It requires meter pulsing equipment at the parent exchange
and is hard wired in the line before the first telephone instrument for both hard wired
and phone socket installations.
Made by Landis & Gyr Lake
Beech House, Green Hill Road, Tallaght, Dublin 24
Telephone: 0001 515 422
BT supplied on rental terms only.
APPROVAL STATUS
Approval No. S/1000/GF/1981/PR
Installation and Operating Instructions supplied with new Meters 47A.
Ashdown can be fitted on a direct exchange line or the extensions of through fed PBX's
i.e. those with a metallic path through the central switching equipment.
The serving exchange must provide meter pulses.
Ashdown requires the connection of a telecommunications earth.
PARTS
| DESCRIPTION |
BT ITEM CODE |
| Meter 47A |
373890 |
LINE TESTING
Normal test conditions. A line current of 25 to 100mA is required when the telephone is
off hook to produce 6 to 7 volts across meter (Blue & Red cord conductors) to provide
dc power to enable the meter to operate to exchange SPM meter pulses. The line must be
provided with metering equipment in the serving exchange.
ADDITIONAL INFORMATION
Meter specification:-
Line current - 25 to 100mA required to operate.
Power drain - Zero when idle. Typically 6 to 7 volt drop across meter A & A1 (Blue
& Red cord conductors) when a call is in progress.
SPM Pulse - 48 to 51 Hertz. Critical to frequency, phase and shape.
SPM Min level - 33 volts per wire in phase. (Approx. 0.3mA A & B wires).
Min Pulse duration - 130mS i.e. 6.5 cycles at 50HZ.
Max metering rate - 1 pulse per second.
Brief description of operation:-
With the telephone off hook, line current flows through the meter A & A1 terminals of
the meter and a voltage of about 7 volts is developed. This voltage is used to power all
the circuits within the meter and charge a 47uf capacitor. Both the mechanical indicators
are connected in parallel, in series with the 47uf capacitor and the output of a pair of
transistor.
When a meter pulse is received, it is validated for voltage, frequency, duration, equal
presence on both wires (longitudinal pulse) and shape. The pulse shape must be nearly
sinusoidal otherwise it will be rejected. With the meter pulse validated as good, the
output transistors will turn on and the 47uf capacitor discharge through both indicator
coils. The capacitor takes approximately 1 second to recharge for further operation.
Problems
Where intermittent non operation of a meter is being investigated, joint tests with the
exchange should be carried out to prove whether the meter is not responding to a
particular SPM relay set/s in the exchange. SPM relay sets are intended to send 50 Hertz
pulses of 130 - 190 milli seconds (ms) duration of 40 to 60 volts RMS. to line. SPM pulses
may be observed by connecting a meter multirange in series with a capacitor of 1 to 2uF as
shown below. The test meter should read approximately 40 to 60 volts AC between either
wire and earth. Pulse duration measurement should be carried out by the exchange staff
using timing equipment and should not be less than 130 ms. Another critical factor is the
pulse shape, it should be sinusoidal. If mis-operation occurs then it may be necessary for
the SPM/MCE equipment power unit at the exchange to be checked to see if the filter unit
has been strapped out as per Works Specification TE 40036, paragraph 7. The Filter Unit is
a large series connected inductor, and when connected flattens the peaks of the meter
pulses making them appear to the Ashdown not sinusoidal. therefore not acceptable, and
Ashdown will not operate.
Connect to A & B wires in turn.
BT Earth ---- Capacitor (1uf to 2uf) ----- Meter on 10OV AC
Test Meter will indicate about 50 volts to on each pulse.
If non or intermittent operation is still apparent at the customers premises after all the
above tests have been tried and proved satisfactory. then the problem is almost certainly
due to High Frequency (H.F.) noise being superimposed on the meter pulse on the line and
distorting it. This inference can be picked up almost anywhere and localisation can be
difficult.
If this problem is suspected, an Ashdown should be modified locally by fitting a 33nF
capacitor, (63 volt AC working) across resistor Rll and another across R14. These act as a
low pass filter to H.F. interference and reshape the meter pulse before it is applied to
the base connections of transistors TR3 & TR4. If the meter works after modification,
you have proven beyond doubt that there is no fault in the exchange metering equipment or
the Ashdown meter, but there is a problem of induced interference somewhere along the
line.
The modification described is not approved, therefore the modified unit should not be left
connected. The problem has been identified and the corrective action required can now be
decided at District level.
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