Immunity of HT200 against short power dropouts

The terminal with 7“ touchscreen, HT200, is used as a HMI in building technologies. It is powered by a DC voltage of 9-36 V, typically 12 or 24 V. The power supply is not included, as the stabilized power supply in the panel is usually used. When specifying the power supply, several parameters which may influence the correct functionality must be taken into account.

First of all, the nominal output power of the supply must be selected regarding all components to be powered. It is mostly the I/O modules which must be considered according to their peak consumption if all the output relays are activated. The difference between a typical I/O module or compact controller consumption and its possible maximum consumption may be hundreds of percents, e.g. a MCIO2 is consuming 2 VA with relays off, and 5 VA when all digital inputs are activsted and all relays energized.

Another important feature is how the power supply behaves after a short power dropout. Thanks to the output capacitors, a dropout of several milliseconds at the input of the supply (230 V AC) results in a slow decrease and following increase of the output voltage.  This may result in the internal HT200 power supply staying off.  The LCD display and green Power LED are dark. To restore the functionality, the external power supply must be completely disconnected and connected again.

The HT200 was tested according to ISO 7637-2 Road vehicles – Electrical disturbances from conduction and coupling – Part 2: Electrical transient conduction along supply lines only. Although the device is not primarily designed for installations in road vehicles, it proved compliance with all tests of the standard except for the test pulse No. 4. This pulse represents a voltage drop in a power grid

after a vehicle starter is activated. This pulse type is very similar to a short power outage in a distribution panel:

test_puls_4

 

The parameters of the pulse are specified in the standard; just for information: at 12 V DC the drop is  Us = -6 to -7 V lasting about 40 ms.

In case the HT200 shows the above described symptoms, please check the power supply properties and select a power supply (and its load) which prevent the system from the short-time dropouts at the power supply output (12 V).

[1] Data sheet HT200, Domat Control System, 2016

[2] ISO 7637-2 Road vehicles – Electrical disturbances from conduction and coupling – Part 2: Electrical transient conduction along supply lines only