Ametek DPA1 Series Installation, Operation And Troubleshooting Instructions page 24

Operation
Figure 3-4 Comparison of Resistivity/Temperature Characteristics of Common Heating Element Metals
Figure 3-5 Resistivity/Temperature Characteristics of Typical Silicon Carbide Heating Element
3-22. The range of current limiting action is between 25 percent and 125 percent of the rated current output
of the PHASE/AMP. For load exhibiting a 5:1 resistance change ratio (cold to hot resistance), an initial setting
of 100 percent to 125 percent of the CURRENT LIMIT control can usually be used safely. For loads exhibiting
an 8:1 or greater cold to hot resistance change ratio, an initial CURRENT LIMIT control setting of 50 percent is
recommended. The setting may be increased if the heating element does not draw excessive current during
cold start-up.
3-23.
The CURRENT LIMIT control should not be set below a point that would limit the output current to less
than 6.5 percent of the current that would be demanded if no limiting existed and full rated output Voltage were
present across the load. This could occur if the load resistance change ratio is 15:1 from cold to hot, or if the
load is not intended to sustain full line Voltage and the Current Limit is used as a current control. Setting the
CURRENT LIMIT control below the 6.5 percent point is a misapplication of the equipment, and may result in
system oscillation and damage to the PHASE/AMP or the load. Consult the factory.
18 AMETEK HDR Power Systems
Phase/AMP Series DPA1/DCPA1
Document 9100030