timers with two operating signals !!

sometimes i find some timers with two operating signals as the first is : A1 & A2 and the second is : B1 & B2

A1 & A2 is an input voltage to the coil of the timer as 24 vdc

B1 is an output voltage from the timer as also may be + 24 vdc

B2 is the return signal for B1


i can operate this timer by the normal timer i.e : one signal as only A1 & A2

as i can connect B1 to A1 and then B2 will be A1 : i.e : i make a bridge between A1 & B1 and i connect the terminal which must connected to B1 to be connected to A1 for the normal timer with only one operating signal !!


the question now : why do we use two operating signals ??


what is the advatnage for using two operating signals ??



thanks

Without knowing what product you are talking about, I can only assume that the item is some sort of Safety Timer. It monitors two input signals. We use them for time delay resets on Category 4 safety.

i found these types of timers for siemens products or pilz products


i agree with you it may be only safety , but i found these types of timers are used in wide range , and as i told if this timer is damaged or defected i can put another timer but by only A1 & A2 !!

Thanks

I know PILZ is a safety specialty company. They are used in many of our European machines.

Could you post a part number of the timer you are talking about, I'm sure we could help ease your confusion if we knew exactly what you were talking about.

the timer is off delay timer from PILZ company , its part number is :

PF-lWB/FZ/24VGSWS 2UZ

the item lWB may be 1WB i am not sure now because this timer is not aviliable now for me

as i told before i can achieved this requriment safety by only use A1 & A2 as i said " i can connect B1 to A1 and then B2 will be A1 : i.e : i make a bridge between A1 & B1 and i connect the terminal which must connected to B1 to be connected to A1 for the normal timer with only one operating signal " !!


So why do we use two operating signals ??


what is the advatnage for using two operating signals ??



thanks

i want to tell you also , i found safety realyies - in additional to the off delay timer - from PILZ as PNOZ family as also they have two operating signals

and i also can achive the same requirement safety by using only A1 & A2 for this relay as i described before

thanks

One usage I've seen is where you use the NC contact as part of the safety circuit the other signal (NO) used to signal the controller to generate an alarm indicating the fault location. Come across several Xray machines for example that have this configuration

The two signals are used when there are two separate signals that must be monitored to provide the safety level required.

Some devices have the option to wire them using jumpers to make it operate with only one signal, this is for when there is only one required signal that needs to be monitored.

It allows one product to serve multiple purposes for the customers needs.

Just because you can operate with one signal by using the jumpers, does not mean that your machine should use it. Whether or not you need one or two depends on the layout of your machine and the safety level you are looking at using.

If you ever have a question about the proper use of a safety device, the companies provide help. They will even help design your safety circuit and make sure it means all requirements.

ther is also the possibility to have a category 3 safety circuit (intrinsically safe level) that requires multiple contact usage. This can easily combine with a category 4 stop in this case that timer is great for this app. more info on these category circuits can be found on the Seimens website
http://www.ad.siemens.de/fea/html_76/down_module.htm

thanks

The timers with A1/A2 and B1/B2 are usually 'Off delay' / 'Off pulse' timers with permanent supply. The A1/A2 are the supply terminals and B1/B2 are the timer trigger terminals. There are a few of advantages over 'true off delay', they are usually cheaper, can have much longer time ranges as you aren't relying on a battery and they can be reset by turning off the supply to the system.

Bryan

thanks

i agree with you , but i still say i can achieve the same requriment typically by using A1/A2 only as i described before spesially if the voltage for A1/A2 is the same voltage for B1 / B2