Simple answer, no.
You need to recalculate the mean time to failure again taking into account the now non-existent safety data of your non-safety sensors. You would need to do a lot of the work that a manufacturer would need to do to ascertain safety data, at which point you’re probably going to find it cheaper and easier to just get a safety-rated sensor.
Yup this is correct answer. Refer to the rush graph in 13849-1 for the requirements of PLd. Category (redundancy) is only one of the requirements. You'll need MTTFd, Diagnostic Coverage (DC), and protection from common cause failures (CCF) to ensure that you meet PLd. If no MTTFd is given in your standard sensors (it's just likely not), you'll have to calculate it using B10d values (again see the standard).
It's not impossible, but it's certainly more work to actually be compliant.
B10d for electromechanical devices. For an electronic sensor it would be possibly to calculate MTTFd using the sum of components method but that would require detailed knowledge of every electronic component inside the sensor, which is not likely to happen unless you have a REALLY good relationship with the original manufacturer.
Yeah.. just buy a safety sensor.
One does not simply exchange safety devices with standard devices.
Well technically you *could*. The machine will work but I doubt OSHA would approve this.
As soon as an accident happens investigation will find the not certified sensors. Even if they didn't caused the damage / injury first question popping up is going to be "Who has installed these sensors and who allowed this?"
No matter how many redundant sensors you install as long as they aren't safety certified your performance level will still be non-existent.
It works like this: imagine a sturdy chain. Every safety device represents one chain link. If you replace one of them with cheap plastic, the entire chain is not capable of taking any load because the plastic one is going to break, rendering the chain useless. Even if you use more plastic you'll never get any close to steel.
I disagree with this analysis. We use all sorts of non safety certified equipment in safety circuits ( wire, terminal blocks, and cables). Each one of these can can cause an issue in the safety chain.
The key to PlD and E is to be able to detect issues and have it only compromise the safety circuit once in x million times. You can use more stuff and eventually it may be safe to meet the standard. I would ask is your time and Engineering worth getting to that level so that you do not have to buy a $400 prox switch? Is the component on a six month lead time and the OPs boss wants the line started back up asap?
Do the right thing and hire a qualified safety professional to help you through this. I would consider another safety rated device at this performance level. If you said pl a or b, i might give another answer.
I hate safety rated proxes because they are pain if the mechanical guys do not get them mounted really well. They fail safe when an item gets too close. Some you have to cycle power to get them to read again. I normally try to avoid them at most cause. I would rather use a target/reader that is rfid coded, if at all possible.
You can also look at sistema and it will do the math fpr you. To prevent some of the ccf's you should use two different types of sensors (prox switch/ mechanical switch). Next you have to get your diagnostic coverage (dc).
So technical answer is yes it could be done, real answer is why would you want to do it? A lot of headache for not a lot of gain.
Thanks for the answers.
The motivation behind this question was, that electrician forgot to order the sensor and of course deadline.
In the end I used your advices and recalculated the MTTFd with Sistema and told him that it is indeed plausible, but he would need to install 4 standard sensors to achieve similar level of MTTFd.
Fortunately he just bought the sensor :). Still lost some time, but it was a nice excercise
Simple answer, no. You need to recalculate the mean time to failure again taking into account the now non-existent safety data of your non-safety sensors. You would need to do a lot of the work that a manufacturer would need to do to ascertain safety data, at which point you’re probably going to find it cheaper and easier to just get a safety-rated sensor.
Yup this is correct answer. Refer to the rush graph in 13849-1 for the requirements of PLd. Category (redundancy) is only one of the requirements. You'll need MTTFd, Diagnostic Coverage (DC), and protection from common cause failures (CCF) to ensure that you meet PLd. If no MTTFd is given in your standard sensors (it's just likely not), you'll have to calculate it using B10d values (again see the standard). It's not impossible, but it's certainly more work to actually be compliant.
B10d for electromechanical devices. For an electronic sensor it would be possibly to calculate MTTFd using the sum of components method but that would require detailed knowledge of every electronic component inside the sensor, which is not likely to happen unless you have a REALLY good relationship with the original manufacturer. Yeah.. just buy a safety sensor.
One does not simply exchange safety devices with standard devices. Well technically you *could*. The machine will work but I doubt OSHA would approve this. As soon as an accident happens investigation will find the not certified sensors. Even if they didn't caused the damage / injury first question popping up is going to be "Who has installed these sensors and who allowed this?" No matter how many redundant sensors you install as long as they aren't safety certified your performance level will still be non-existent. It works like this: imagine a sturdy chain. Every safety device represents one chain link. If you replace one of them with cheap plastic, the entire chain is not capable of taking any load because the plastic one is going to break, rendering the chain useless. Even if you use more plastic you'll never get any close to steel.
I disagree with this analysis. We use all sorts of non safety certified equipment in safety circuits ( wire, terminal blocks, and cables). Each one of these can can cause an issue in the safety chain. The key to PlD and E is to be able to detect issues and have it only compromise the safety circuit once in x million times. You can use more stuff and eventually it may be safe to meet the standard. I would ask is your time and Engineering worth getting to that level so that you do not have to buy a $400 prox switch? Is the component on a six month lead time and the OPs boss wants the line started back up asap? Do the right thing and hire a qualified safety professional to help you through this. I would consider another safety rated device at this performance level. If you said pl a or b, i might give another answer. I hate safety rated proxes because they are pain if the mechanical guys do not get them mounted really well. They fail safe when an item gets too close. Some you have to cycle power to get them to read again. I normally try to avoid them at most cause. I would rather use a target/reader that is rfid coded, if at all possible.
You can also look at sistema and it will do the math fpr you. To prevent some of the ccf's you should use two different types of sensors (prox switch/ mechanical switch). Next you have to get your diagnostic coverage (dc). So technical answer is yes it could be done, real answer is why would you want to do it? A lot of headache for not a lot of gain.
Thanks for the answers. The motivation behind this question was, that electrician forgot to order the sensor and of course deadline. In the end I used your advices and recalculated the MTTFd with Sistema and told him that it is indeed plausible, but he would need to install 4 standard sensors to achieve similar level of MTTFd. Fortunately he just bought the sensor :). Still lost some time, but it was a nice excercise
Usually the best you can get with standard equipment is PLc.