Selection of DO (Digital Card) Card

Hi Friends:
what is the criteria and your experienced recommendations if one has to select between these types of DO card:
1- Relay Contact Output Card
2- Triac Output Card
3- Transistor Output Card (Sinking Type)
4- Transistor Output Card (Sourcing Type)

Please, if feel free mail me at [email protected].
Best Regards

You use what you need.
That being said, my preference is to use a DC, 24V, Sourcing output for everything. If I need isolation, higher current capacity, or need to drive 120VAC circuits, I interpose a terminal mount relay block. It is far cheaper (and simpler) to replace the mini-relays in the terminal then replace a relay output module or relay on an output module.

#4 hands down. I try to select output devices that can be driven directly from a transistor output, typically <0.5A at 24VDC. For higher current devices I use an interposing relay as rdrast suggested.

Selection of DO card

Hello Friend:
I m thankful to u for ur quick response. If i have to provide 24VDC in field to an interposing relay of MCC panel and to Solenoid Operated Valve in field, then wat should i select regarding Digital output card?
Y some body select Transistor output card (sinking) or some body select Transistor output card (sourcing)??I m a bit confused? Please help me technically.

Best Regards

Why sourcing? - Simply because it is more 'logical' to most maintenance people that ON = VOLTAGE. With a sinking card, ON = NO VOLTAGE. The other reason I always choose sourcing, is I require that the neutrals and power supply 0VDC connections are all bonded to equipment ground (except for DeviceNet). I find it makes troubleshooting easier.

Use a 24VDC, Transistor output card, sourcing, unless you have special needs. I've even stopped using Triac (AC) outputs except in very special circumstances. In most cases, I find the 24VDC output + interposing terminal mount relay (the real skinny ones) to be more reliable.

One other reason sourcing is used in the industrial environment is that an incidental short to ground (i.e. a smashed piece of conduit or pinched wire) can cause the unexpected or intermittent actuation of machinery devices such as solenoids etc. If sourcing outputs are inadvertantly shorted they will generally prevent this situation (there are of course some exceptions but considerations for this should be included in equipment design to prevent personnel or machine damage)and usually only result in a blown fuse or clamped down power supply.