DeltaV I/O card problem

Thread Starter

nghiadinh94

Joined Apr 4, 2017
7
The card I am having problem with is DO card, 8-Channel, High-Side type. We are trying to use this card's channels to energize the relay NO contact. The card output range is 24 VDC. I suppose 24 VDC for logic 1 and 0 VDC for logic 0. However, we can get 24 VDC for logic 1 and 17 VDC for logic 0, which let us close contact of the relay but not able to open the contact at logic 0 of the program. Has anyone seen this problem before and what can I do about it? Thanks!
 

MrChips

Joined Oct 2, 2009
30,620
This is a high-side switch which means that the output switches the 24VDC to the relay.
Have you tested this with the relay wired in or are you measuring the output voltage with no relay connected?
 

Reloadron

Joined Jan 15, 2015
7,480
You are sure this card is not an open collector pnp output? What happens if you place say a 240 Ohm resistor out there as a load? Do you have a data sheet or part number for the card?

Ron
 

Thread Starter

nghiadinh94

Joined Apr 4, 2017
7
This is a high-side switch which means that the output switches the 24VDC to the relay.
Have you tested this with the relay wired in or are you measuring the output voltage with no relay connected?
Thanks for your reply, I didn't connect it in the card channel, but what I did was to use a voltage generator to test when the relay switch is on at off, and it shows that the voltage when the the NO contact switch to CLOSED is 23.8 VDC and the to OPEN is 8.1 VDC. And since our card channels output 24 VDC max and 17 VDC min, theoretically, the relay would stick at CLOSED position after being switched to CLOSED.
Also, what really does it mean by 'High Side'
 

Reloadron

Joined Jan 15, 2015
7,480
Page 20 of the PDF, they use high side switching. They optically turn on a FET on the +24 volt bus.

High Side Switch.png

Note how the "load" is configured. Place a resistor as I suggested across the load terminals. Just placing a meter out there will not show much as you will see leakage. Place a 240 Ohm resistor across the load terminals and then measure.

Ron
 

JUNELER

Joined Jul 13, 2015
183
Hi,

First try to check the opto isolator and also add an diode across the load(relay).

Second ,swap another relay. since 24v buss is ok, look the ckt that drive the opto.
 

Thread Starter

nghiadinh94

Joined Apr 4, 2017
7
Page 20 of the PDF, they use high side switching. They optically turn on a FET on the +24 volt bus.

View attachment 124019

Note how the "load" is configured. Place a resistor as I suggested across the load terminals. Just placing a meter out there will not show much as you will see leakage. Place a 240 Ohm resistor across the load terminals and then measure.

Ron
Update,
Thanks for your
Page 20 of the PDF, they use high side switching. They optically turn on a FET on the +24 volt bus.

View attachment 124019

Note how the "load" is configured. Place a resistor as I suggested across the load terminals. Just placing a meter out there will not show much as you will see leakage. Place a 240 Ohm resistor across the load terminals and then measure.

Ron
Thanks for your idea, what I did was to just connect the relay in test it, and it works!!! Thanks very much!
 

Thread Starter

nghiadinh94

Joined Apr 4, 2017
7
Page 20 of the PDF, they use high side switching. They optically turn on a FET on the +24 volt bus.

View attachment 124019

Note how the "load" is configured. Place a resistor as I suggested across the load terminals. Just placing a meter out there will not show much as you will see leakage. Place a 240 Ohm resistor across the load terminals and then measure.

Ron
So what is the leakage that you mention? What is the cause of it? And how is it that I have reading of 16.8 VDC at the load channel when having no load resistor connected? Please explain! Thanks very much!
 

Reloadron

Joined Jan 15, 2015
7,480
So what is the leakage that you mention? What is the cause of it? And how is it that I have reading of 16.8 VDC at the load channel when having no load resistor connected? Please explain! Thanks very much!
Reverse leakage current in a semiconductor device is the current from that semiconductor device when the device is reverse biased.
When a semiconductor device is reverse biased it should not conduct any current at all, however, due to increased barrier potential, the free electrons on p side are dragged towards positive terminal of the battery, while holes on n side are dragged towards negative terminal of the battery. This produces a current of minority charge carriers and hence its magnitude is extremely small. For constant temperature reverse current is almost constant though applied reverse voltage is increased up to certain limit. Hence it is also called as reverse saturation current.
The term is particularly applicable to is mostly semiconductor junctions, especially diode and thyristor.
Reverse leakage current is also known as "zero gate voltage drain current" with MOSFETs. The leakage current increased with temperature. As an example the Fairchild Semiconductor FDV303N has a reverse leakage of up to 1 microamp at room temperature rising to 10 microamp with a junction temperature of 50 degree Celsius. For all basic purposes, leakage current is very small, and, thus, is normally negligible.
The above taken from the Wiki is a good explanation. Without any load or just the very high impedance load of your voltmeter you will see "leakage" which is normal. This is why I suggested using a load resistor when checking the voltage outputs. While their drawing is not detailed my guess is what you were seeing with the output off was leakage which is not at all unusual.

Ron
 

MrChips

Joined Oct 2, 2009
30,620
So what is the leakage that you mention? What is the cause of it? And how is it that I have reading of 16.8 VDC at the load channel when having no load resistor connected? Please explain! Thanks very much!
The resistance of a typical DMM when set to measure voltage is about 10MΩ.
Hence with 17VDC reading, you were witnessing a leakage current of about 1.7μA.
This is very normal for a solid-state switch in the OFF state and nothing to be alarmed about.
 

Thread Starter

nghiadinh94

Joined Apr 4, 2017
7
The above taken from the Wiki is a good explanation. Without any load or just the very high impedance load of your voltmeter you will see "leakage" which is normal. This is why I suggested using a load resistor when checking the voltage outputs. While their drawing is not detailed my guess is what you were seeing with the output off was leakage which is not at all unusual.

Ron
Thanks very much for your easy-to-understand answers, I have learned a lot!
 

Thread Starter

nghiadinh94

Joined Apr 4, 2017
7
The resistance of a typical DMM when set to measure voltage is about 10MΩ.
Hence with 17VDC reading, you were witnessing a leakage current of about 1.7μA.
This is very normal for a solid-state switch in the OFF state and nothing to be alarmed about.
Great! I have learned a lot from this! Thanks very much!
 
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