EMS-D120 Ammeter U/S

[Radetzki]

Since the day of installation we have never seen the Ammeter working on the EMS-D120. Current monitoring is carried out with the packaged Ammeter Shunt and utilizing Amps High/ Low inputs on Pin 24/ 25. Two inline FF fuses were added at a later point in time to protect the EMS Current Monitor. Of course all the wiring checkes out fine for continuity and isolation to ground! We are not quite sure if the input to the EMS could have been damaged during the period of system installation. The indication itself does not respond to System Load and just wobbles around the 0 to 1 Amp mark.
Q1: Does anybody know what the input/ monitor limits are on 24/ 25
Q2: What is the input Impedance on 24 /25 ?
Q3: Is the monitor internally protected with a fuse ( onboard )?

Your feedback will be highly appreciated...

Rgds
H.Radetzki

 

[dynonsupport]

If the shunt wasn't actually connected (one of the lines broken, for example), you'd see a little movement around the 0 point. Every time the relay clicks (every 10ish seconds) it would reset to zero.

Do you hear the relay clicking every few seconds?

A couple of other tests...

You can apply a voltage between the ammeter input wires to stimulate it. It's 1 millivolt per amp, so if you put 12V into it, it's going to peg the display, but not break anything. This will let you know that it's working at least.

Also, you can measure the voltage across the ammeter shunt terminals, provided you don't have a super-cheap voltmeter. Again, you should see 1 millivolt per amp, and it should match the display.

 

[Radetzki]

Thank you very much for the promt reply and tipps to troubleshoot the Ammeter. So far the symptoms exactly look like an open cirquit (shunt not connected or one of the lines disconnected). The reading does move arround the zero mark and irregularly displays a value up to +/- 1amp but unrelated and non responsive to any load applied or changed! There definately also the "click" of the internal Relay to be heard every 10 seconds after wich the current indication resets to zero.
Again the wiring installation checks out perfect when tested with an VMO for cuntinuity as well as isolation to ground. Strange enough the Ammeter does actually peg to Full Scale when the + Amps lead is hotwired to the Positive Battery Termanal. One more thing to mention would be that the circuit location of our Shunt is between Structural Ground and the Neg (-) terminal of the Battery. Yes we know that is not according to the installation manual and the recommendation, but we thought a lot about it and did it deliberately. Since only the voltage drop accross the Shunt alone should be the parameter for proportional current and not its potential towards Structural ground. But please correct me if I'm wrong, or if there is some unusual signal processing within the box. Vdrop accross the shunt measures out fine with varying loads, e.g. switching Landing/Taxi Lights or Boost Pumps on or off, but no display.

 

[dynonsupport]

Unfortunately, it's not going to work on the negative side of the battery.

In technical terms, we need the common mode between the terminals to be between 10-30V, which it won't be where you have it.