ekm- und hm-Rechner II

am Fu.M.G. 39TD (Flak) (=Würzburg 62D)

Firmenschrift Elt 508


Nur für den Dienstgebrauch

September 1944

Analogue computer for GL (Flak) control, in conjunction with Würzburg FuSE62D


The wartime product-code 'Elt' might stand for: F. Kment, Maschinenbau Prag(ue) XIX, Piettova 180. Kment sounds a bit German, and could have been a subsidiary branch of a German company.

Please notice that for practical reason, I have kept the drawings (Anlagen) separate from the text section of this manual, as some of them are having size A1 and A2, which otherwise would have created enormous broad pages where (landscape) DIN A1 schematic is concerned, whereas the normal sized (portrait) A4 pages are hardly readable!

Please notice also:

F 027-1


F 027-2

Recently added onto our website being part of the Würzburg Werkstattbuch (Würzburg service collection) Please notice the sections: E 01 and E 02 as well as the F 001 - .. series!


Anlage 1, size A3 (drawing number 1)

Anlage 1 (PDF)

Interesting is that the data is fed onto two different users. The obvious Flak predictor, called 'Kommandogerät' and towards the 'Beobachtungstisch ek - h - G'. I believe meant is here the well known "Seeburgtisch". A square glass table (plate) where from beneath data was projected as to correlate with the map printed on the frosted (stained?) glass window. It might also have been possible to steer data projectors used in the huge command bunkers.


How did it actually work?

The basic principle of what should be achieved

The value of 'e' is called, in modern terms, slant range. Constituting the distance towards the target. The value of 'e k' means the target distance projected on a map, between radar set and its virtual position at the map. When the elevation angle γ (gamma) is 0 degrees, the map projection of the target equals the one read-off the radar screen. When γ is becoming 90 degrees, the map distance is, logically, 0 m.      k stands for: Karte (map) e for Entfernung (distance)




Der elektrische ekm-  und hm-Rechner hat die Aufgabe, aus der am Fu.M.G.39TD (Flak) anliegenden Meßwertentfernung em und dem Meßhöhenwinkel γM die Meßhöhe hM und die Meßkartenentfernung ekm zu errechnen.

Hauptsächkliche Eigenschaften

Die von den am Fu.M.G. 39TD (Flak) angebauten Rechenteilen ermittelten elektrischen Werte werden an einem vom Fu.M.G. 39TD (Flak) abgesetzten Abgleichgerät in mechanische Drehwerte umgewandelt und zur Steuerung von Gebern des Übertragungsgerätes 37 verwendet.


Technische Daten

Bereich für die Kartenentfernung eKM    5 - 195 hm*

Bereich für die Meßhöhe hM    5 - 195 hm

Der e-Meßbereich des Fu.M.G. 39TD (Flak) beträgt etwa 400 hm (40 km, AOB) und wird durch die kleineren Meßbereiche des eKM und hM-Rechners II nicht beschränkt. Der e-Bereich von 200 bis 400 hm wird jedoch nicht richtig in die entsprechenden eKM- bzw. hM-Werte umgerechtnet. Auf die Erfassung dieser Größen, die praktisch wenig in Frage kommen, wurde aus Genauigkeitsgründen verzichtet. Die erreichbare genauigkeit für die Werte eKM und hM bertägt 4 ‰ der Endwerte.

Speisespannung des Rechners    110 V 500 Hz

Gesamtstromaufnahme des Rechners (110 V 500 Hz-netz)    ca. 1,6 A

Die Speisespannung wird von einem im Betriebskasten 39T eingebauten Umformer U94 geliefert.

It is quite understandable, that Flak defence has to rely on predicted parameters. The travelling time of a flak shell is often approximately 20 s. The system was thus aiming at targets which might likely arrive at a certain spot 20 s later. Hence, every kind of system inaccuracy must be prevented. Let us consider, for better understanding, an aircraft having a speed of, say, 360 km/h which is equal to 100 m/s; within 20s this aircraft has moved already 2000 m! The impact of flak shells is not only achieved by a direct impact, but also by means of nearby shell bursts owing to the timer controlled fuse inside the shell. The timer has a double function, one explosion at a given (flight) level (altitude), though secondly it had to prevent collateral damage at the ground from returning unexploded Flak shells! But 20s is only the travelling time of the flak shell itself. First, a target has to be measured by radar - its data has to be conveyed onto the predictor (Kommandogerät) - Flak parameters had to be computed and being passed onto the GL site -  here the operators had to set the shell fuse timers appropriately - the shell has to be handed over to the gunners - the gun had to be loaded and directed accurately and at the right moment the shell(s) had to be fired!

*The German gunnery, particularly Flak measured ranges in hecto meters (hecto = 100); 195 constitute thus 19500 = 19.5 km


Anlage 2 (Schematic 2)

Potentiometer I is inside the fine range measuring system (in Anlage 3 in the top box on the left hand side, having a value of 10 Ω, integrated into the 'e' data servo module shown on page 14 of the pdf maual). Its output voltage is fed in parallel onto the sine and cosine potentiometers II and III inside the SC-box (Getriebe), which mechanical data is derived from the antenna elevation angle. Their outputs are fed onto two equal servo amplifiers, which directly ran at 110 V 500 Hz. As the systems are symmetrical and all being fed from the same ac source, the ac supply component is being  neutralised. The output of both amplifiers (V445) are loaded by means of a Ferraris motor 'M". This is a motor type responding on two 90° phase shifted signals and can have a very slow angle velocity at will and will hold when appropriate. For a very long time, this principle was (is) also used in electricity-consumption counters. G1 and G2 both provide information on the rotation speed versus time, and act as feedback (known as: Tachometer). The actual position is detected by means of the feedback potentiometers P IV and V, as to guarantee the true angle (phase) reproduction. 


I learned the name of a (curious) kind of connector used in Flak and related control systems. Even Rehbock uses one. I know now that these typical connectors were called: 'Renkstecker'* and 'Renkdose' (the latter is the chassis part) followed by a number. This number might provide the number of connector pins. The suffix characters might give the pin-layout. Some heavy connectors are having rather strange configurations. I believe, this was done as to ensure that connections are being made correctly under all possible circumstances. Normal connectors hardly have this safety feature build in. For instance, when we have a say 24 pin connector type, then every equal connector can be interconnected, but this might eventually cause heavy damage. Here every system had its own male versus female configuration (as long as the sum of pin numbers is constant)! Thus each connector consisted of a typical configuration of male and female pins on either side. Hence, we can now no longer think of the male or female side of a cable. *Searching recently for 'Renk' on Google, I discovered that this company still make connectors


Anlage 3, the full schematic of the system

Anlage 3 (PDF)



Anlage 4

Anlage 4 (PDF)


Anlage 1 (PDF)

Anlage 2, is copied from my book on Wurzburg: Deckname Würzburg

Anlage 3 (PDF)

Anlage 4 (PDF)

Anlage 5 (PDF)

Anlage 6 (PDF)

Anlage 7 (PDF)

Anlage 8 (PDF)

Anlage 9a/b (PDF)

Anlage 10a/b (PDF)

Anlage 11a/b (PDF)


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