Dutch PTT clock

With a movement by CTW (Carl Theodor Wagner).

• Usually 1 pulse per minute, but 1 every 30 seconds also occurs!
• Movement adjustable for 60, 48, and 24 volt pulses
• Pulses must alternate: positive and negative in turn.
• The movement in the photo above is from 1961.

Our 12/24V pulse generator can generate a maximum of 24V pulses. The movement features four screws that allow one or two connecting bridges to be attached in various ways. This allows you to select the pulse voltage at which the clock operates.

If the original jumper bridges are missing, a bridge can easily be made with a small piece of copper wire.

Measuring resistance

Use a multimeter to measure the resistance of the movement, as an indication of whether it is still in good condition and which voltage it is set to.

Ensure that the movement is not connected when measuring, and measure the resistance at the connection points of the movement.
The measured resistance is expressed in Ohms, symbol Ω. Values higher than 1000 are often expressed in kilo-Ohms (k = 1000). 4500 Ω is then represented as 4.5 kΩ.

• 1 kΩ to 3.5 kΩ : 12 volt pulses
• 3.5 kΩ to 5 kΩ : 24 volt pulses
• 9 kΩ to 11 kΩ : 48 volt pulses
• 14 kΩ to 16 kΩ : 60 volt pulses

Very low values of the resistance may indicate a defect such as a short circuit. A resistance that is too high (greater than 16 kΩ) may indicate a defective coil, or a loose electrical connection between the terminal and the coil.

Batteries

An indication* of how long a clock can run on a set of batteries:

• Pulse frequency 1 min: 2 years
• Pulse frequency 30 sec: 1 year and 4 months

The movement determines whether the pulse frequency is 1 min or 30 sec. Measured with a pulse length of 150ms.

*) All clocks are slightly different.