Power switching elements

LA724I and LA724I HP power output modules

• Power triacs with zero crossover switching
• Protection of triacs and opto-triacs against overvoltages by Transil diodes

LA724I SSR power output module

There are no power triacs here. The load is activated via external Solid State Relays (SSR).

Output power

LA724I power output module

• 24 power channels of 230 V each (8 outputs per phase)
• Max. 1 150 W switching capacity per output
• Max. 7 360 W switching capacity per phase

LA724I HP power output module

• 12 power output channels for 230 V/400 V (4 outputs per phase)
• Max. 2 300 W/4 000 W switching capacity per output
• Max. 9 200 W switching capacity per phase for star connection and max. 16 000 W switching capacity for delta connection

LA724I SSR power output module

24 channels with one digital control signal of 24 V (8 outputs per phase)

Forced ventilation

LA724I and LA724I HP power output modules

Depending on the switching capacity and ambient temperature, the power output modules may have to be forced ventilated. A fan module is available as an option for this purpose, see "Fan module".

For detailed information, refer to the "SIPLUS HCS724I Heater Control System" Operating Instructions, http://support.automation.siemens.com/WW/view/en/55336534.

Temperature monitoring

LA724I and LA724I HP power output modules

There is an NTC thermistor on the heat sink for monitoring its temperature. This temperature-dependent resistor outputs a signal to the SIMATIC S7?300 at 92 °C ± 3 °C. A second switching threshold at 100 °C ± 3 °C switches off the power outputs of the module.

Supply voltage monitoring

LA724I SSR power output module

• The connected 24 V DC supply is monitored for failure. In the event of a failure, the outputs to the Solid State Relay (SSR) are deactivated.
• The drivers for the control outputs are monitored for correct functioning.

Fuses

LA724I power output module

• Each power output has a 5 A fuse in a fuse holder that is accessible from the front to protect the power triac, and one 32 A fuse per phase to limit the phase current.

LA724I HP power output module

• Each power output has a 10 A fuse in a fuse holder that is accessible from the front to protect the power triac, and one 40 A fuse per phase to limit the phase current.

LA716I SSR power output module

Protection for each channel is to be provided externally.

Diagnostics facilities

LA724I and LA724I HP power output modules

Diagnostics functions are provided as standard to detect the following faults:

• Internal fuse defective or triac at high-resistance
• Triac failed
• External fault such as blown fuse, heat emitter or cable breakage

If several heat emitters are connected to one output in parallel, failure of an individual heat emitter is detected by means of extended diagnostics.

LA724I SSR power output module

Two different diagnostics methods are possible:

• Diagnostics of voltages from the load circuit allows the following faults to be detected:
  • Solid State Relay (SSR) cannot be closed, supply line to the SSR is interrupted, or external channel fuse has ruptured
  • Solid State Relay (SSR) cannot be opened, break in emitter or wiring
• Diagnostics using the external current measuring module (see "Current measuring module") allow the following faults to be detected in addition (these diagnostics are recommended for fault detection in emitters connected in parallel):
  • Rated voltage for channel has been exceeded
  • Rated voltage for channel has been undershot