The ZK I is a mechanical six-place period delay mechanism whose electromagnet ope-rates at 8 to 12 volts and 0.2 ampere. The time for the completion of one step-up cycle after actuation is approximately 40 seconds. The ZK I was developed for the M 1 mine unit and was replaced by the improved ZK II.

Figure 287 – ZK II

The ZK IIa is the same as the ZK II, except that the tome interval is increased from two minutes to four minutes.

The ZK IIb is the same as the ZK II, except that the electromagnet operates off the microphone battery at three to four volts and 0.5 ampere. This clockwork was used with the AT 1 and AT 2 mine units.

The ZK IIc is the same as the ZK II, but is designed to operate on a very short elec-trical impulse. This modification enables the ZK IIc to be used with the MA 2/3 mine units and to operate after the magnetic and acoustic systems have been activated.

This device was under development at the close of the war, and no information is available.

The ZK IIe (figures 288, 289) is a specially modified period delay mechanism used with the MA 1st Mine unit. It is operated by the Magnetic system of the MA 1st. A magnetic actuation starts the ZK, and after 15 seconds, cam A opens the normally closed switch A for approximately 2 minutes. If a proper acoustic actuation does not occur in the 15-second interval, the mine will not fire because switch A re-opens, de-energizing the acoustic component. After 84 such actucations cam B closes switch B permanently, put-ting the acoustic system in the cirucit.

Figure 288 – ZK IIe, Switcher

Figure 289 – ZK IIe

The ZK IIf is the same as the ZK II, except that the time interval is decreased from two minutes to five seconds.