Operating instructions

2.5.2. LOAD MONITORING

It is possible to monitor load by absolute monitoring of heating elements with R

hot

cold

≈ 1 and

relative monitoring of heating elements with R

hot

cold

≠ 1.

2.5.2.1 ABSOLUTE VALUE MONITORING CURRENT

This function allows monitoring of a freely selectable absolute current limit. The parameters for

the value may be set in ampere.

This absolute value monitoring lends itself to one or more load resistances organized in parallel or

in series. Generally, the effective current value measured is continuously compared with a preset-

table absolute current limit for undercurrent or overcurrent. If these limits are undercut or exceeded

an indication occurs after Tv =10 mains periods. In case of resistor elements organized in parallel,

it is therefore possible, using the lower current limit, to detect a partial load interruption. Using the

upper current limit, in case of resistors switched in series, short-circuiting of an element may be

detected.

2.5.2.2 RELATIVE MONITORING

This monitoring is sensible if the resistance value of the load slowly changes. Changes in resistance

may for instance be caused by temperature changes or by ageing. The current (b) of the Power

Controller is regarded as 100% load current (current in fault-free state) after activation of the RESET

or CONTROLLER LOCK. The RESET is automatically activated after each startup, restart or after

mains outage. In case of relatively slow changes of the current, due to characteristics of the above

mentioned heating elements, automatic adjustment of the internal reference value to 100% is

performed (b‘).

Quick current changes, which may for instance occur in case of partial short-circuit, may be

detected by overcurrent monitoring (max., a – a‘).

Quick current changes, which may for instance occur in case of load breakdown may be detected

by undercurrent monitoring (min., c – c‘).

I < threshold

indication 16,17 (Chap. 3.4)

FIG. 4: ABSOLUTE VALUE MONITORING

FIG. 5: RELATIVE MONITORING