Ea Elektro Automatik EA Elektro-Automatik EA-ELR 9750-22 3U Electronic Load 0 - 22 A 0 - 750 V/DC 0 - 3500 W 33200404 Data Sheet

Page 71

EA Elektro-Automatik GmbH

Helmholtzstr. 31-33 • 41747 Viersen

Germany

Fon: +49 2162 / 3785-0

Fax: +49 2162 / 16230

3.10.2.4  Operating the master-slave system
After successful configuration and initialisation of the master and slave units, these will show their status in the 

displays. While the master merely shows “Master” in the status area, the slave(s) will continuously show like this, 

as long they are in remote control by the master:

It means, as long as a slave unit is in control by the master, it won’t display 

any set values, but actual values, and it will show the DC input status and 

possible alarms.

The slaves can no longer be controlled manually or remotely, neither via the analog nor via digital interfaces. They 

can, if needed, be monitored by reading actual values and status.
The display on the master unit changes after initialisation and all set values are reset. The master now displays 

the set and actual values of the total system. Depending on the number of units, the total current and power will 

multiply. The following applies: 
•

The master can be treated as a standalone unit

•

The master shares the set values across the slaves and controls them

•

The master is remotely controllable via the analog or digital interfaces

•

All settings for the set values U,I and P (monitoring, settings limits etc.) will be adapted to the new total values

•

All initialised slave will reset any limits (U

Min

, I

Max

 etc.), supervision thresholds (OVP, OPP etc.) and event settings 

(UCD, OVD etc.) to default values, so these don’t interfere the control by the master

•

If one or more slaves report an device alarm, this will be displayed on the master and must be acknowledged 

there so that the slave(s) can continue operation. If the alarm had caused the DC input to be switched off then 

this will be reinstated automatically by the master unit once the alarm has been acknowledged

•

Loss of connection to any slave will result in shutdown of all DC inputs, as a safety measure, and the master 

will report this situation in the display with a pop-up “Master-slave safety mode”. Then the MS system has to be 

re-initialised, either with or without re-establishing connection to the disconnected unit(s) before.

•

All units, even the slaves, can be externally shut down on the DC inputs using the pin REM-SB of the analog 

interface. This can be used as some kind of emergency off, where usually a contact (maker or breaker) is wired 

to this pin on all units in parallel.

3.10.2.5  Alarms and other problem situations
Master-slave operation, due to the connection of multiple units and their interaction, can cause additional problem 

situations which do not occur when operating individual units. For such occurrences the following regulations have 

been defined:
•

If the DC part of one or more slave units is switched off due to defect, overheating etc., the whole MS system 

shuts down the power consumption and human interaction is required.

•

If one or more slave units are switched off on the AC side (power switch, supply undervoltage) and come back 

later, they’re not automatically initialised and included again in the MS system. Then the init has to be repeated.

•

If the DC input of the master unit is switched off due to a defect or overheating, then the total master-slave system 

can take no input power and the DC input of all slaves is automatically switched off, too.

•

If the master unit is switched off on the AC side (power switch, supply undervoltage) and comes back later, it 

will automatically initialise the MS system again, finding and integrating all active slaves. In this case, MS can 

be restored automatically.

•

If accidentally multiple or no units are defined as master the master-slave system cannot be initialised.

In situations where one or multiple units generate a device alarm like OV, PF or OT following applies:
•

Any alarm of a slave is indicated on the slave’s display and on the master’s display

•

If multiple alarms happen simultaneously, the master only indicates the most recent one. In this case, the particu-

lar alarms can be read from the slave units displays. This also applies for remote control or remote supervision, 

because the master can only report the most recent alarm.