Replace relay with sinking output (non)

[eight_bools]

I’ve got some devices that are triggered by shorting pins to common. There is 24 volts on each pin and right now I am using a relay output card in a SLC rack to do this now.

I think this is called BCD, as you can select a number up to 127 by combining relays.

I am putting together a new system with Point IO hardware and the most relay outputs I can find for the 1734 series is a 4 relay output card. So i would need 2x output cards per device which would add up quickly. I was wondering if a sinking output card would do the same thing. It’s my understanding that a sinking output would pull the output to the common terminal.

Anyone have any experience or advice on this? Title was supposed to be NPN, auto correct got me again.

[TheWaterboy]

solid state outputs have some leakage so you might have to add pull down resistors to compensate for that.

[I_Automation]

Actually changing over to a sinking output would be good for this, and the transistor outputs usually last longer than the relays in the existing cards. Plus if this is in an office or in your house the noise of relays clicking can be enough to turn the PLC off until you get DC outputs. [Speaking from experience - the first PLC I setup for the lights on my Christmas tree was all relay outputs, had to shut that off within 15 minutes]


Just buy some resistors and add them from the start as TheWaterboy says.

[DaDaDadeo]

I've been using transistor outputs with 6mm slim relays. The cost of a transistor output card and 6mm relays combined is usually less than a relay card by itself. Custom interlocks, power feeds, and voltage differences are far more flexible. The control box real estate taken by the relays is minimal. The usual current draw is up to 6A for each relay.

[GaryS]

Rethink what you are doing
Sinking Output / Inputs are frowned on in the industry a ground fault can cause an inadvertent input to be on and cause problems in the control
In all cases it would try and avoid sinking inputs I have seen many problems with them
The BCD you talked about is ( Binary Coded Decimal ) it’s only a way of displaying a number in your case 0 to 127 lower 7 bits on.
Another common way they display a number in ASCII string
Just keep in mind with all computer data you must know how to understand the bit pattern to understand the word / number
If you are having problems with the relay contacts try switching to Gold Plated contact relays they are designed for low current applications, they self clean when the relay pulls in. most relay contacts used today are cadmium they require a larger current flow to pass through and can have problems with very low currents

[eight_bools]

Originally Posted by I_Automation

Actually changing over to a sinking output would be good for this, and the transistor outputs usually last longer than the relays in the existing cards. Plus if this is in an office or in your house the noise of relays clicking can be enough to turn the PLC off until you get DC outputs. [Speaking from experience - the first PLC I setup for the lights on my Christmas tree was all relay outputs, had to shut that off within 15 minutes]


Just buy some resistors and add them from the start as TheWaterboy says.

Another case of if I had just read the manual I would have found the answer that I was looking for. It has an example of using an NPN "external device." Doesn't show a resistor though, how would I calculate the resistance that I need? (that seems like something I should know anyway)

Anyone have experience with using 12v devices on the 1734-OV4E? It says 10-28 volts for input and the minimum voltage for an output being 10v. I am using a Patlite voice annunciator which works on 24vdc but the PA (separate device) uses 12VDC and uses the same type of trigger, shorting the input pins to common.

[I_Automation]

Originally Posted by eight_bools

Anyone have experience with using 12v devices on the 1734-OV4E? It says 10-28 volts for input and the minimum voltage for an output being 10v. I am using a Patlite voice annunciator which works on 24vdc but the PA (separate device) uses 12VDC and uses the same type of trigger, shorting the input pins to common.

I use 2 cards of DC outputs with my 12V solar batteries to control 12V lights with no problem. Plus one NPN card does control 12V and 24V circuits with the 0V tied together from the batteries and 24V power supply.



I even had a ML1400 with DC IO ready to go to "interfere" with the way my SUV controlled all the lights, and add a GetOutOfMyWay flashing mode - but a drunk driver totaled it for me before I got to until it and the new SUV has a weird setup for parking and taillights (no separate bulbs, it gives the turnsignals & brake lights 6.5 volts to light them up dimmer)


The reply above about NPN output devices can be activated by the wire grounding out is a valid issue, but I deal with a lot of machinery from Europe & Asia and they ALL use NPN exclusively - the engineers all think NPN devices respond faster so that's what they use, but when I point out the PLC in the machine only scans once every 0.05 seconds (1/20 second) a device responding 0.0002 seconds quicker is not going to be noticed 99.99% of the scans.

[eight_bools]

Originally Posted by I_Automation

I use 2 cards of DC outputs with my 12V solar batteries to control 12V lights with no problem. Plus one NPN card does control 12V and 24V circuits with the 0V tied together from the batteries and 24V power supply.

Was wondering how the wiring would work if I was using a 1734-OV8 output card. If the power comes from the backplane would I need to use one of the 1734-FPD modules to separate it from the 24v on the backplane?

[I_Automation]

Yes, either need a bank of 8 interposing relays for the -OV8 or isolated inputs.

Unless you have the RemoteIO card using 8 mini-DIN mount relays would be less costly.

The cards I use are in SLC racks.