Can we connect duel element thermocouples in parallel so as not to trigger fault upon one failure ? Normally dual element thermocouples we connect the loop with one element and other just keep it as stand-by , upon failure of the connected sensor we take up an urgent maintenance activity to connect the redundant good sensor to bring back the measurement loop back ! Wondering if we can connect both in parallel upfront ?
Thermocouples are widely used in the temperature measurement of power plants, refineries, petrochemical and other oil & gas applications. There are umpteen number of temperature measurement loops which are very critical for the process and safety systems.
Say for instance if you use Thermocouple in a critical PID control loop the failure of Thermoscope could lead to control loop failure (I know that systems come with 2 out of 3 Thermocouple elements these days ; assume you have one dual element Thermocouple) or in the case of protection (safety) system the controller trigger protective action as a result of measurement failure.
Its well known that systems comes with fault tolerant measurement loops such as 2OO3 measurement loops in the modern instrumentation systems, even in those cases we have to simulate the other loops while doing the live maintenance on the faulty loops so as not to trigger one more loop faulty. Even with the 2OO3 redundant measurement loop, Process engineers feel uneasy when you have one measurement failure; unless you rectify the issue immediately your reliability dependence goes back to only one transmitter (NO I don’t think anyone have ever implemented 1 out of 3 logic). There are certain process systems whereby its not very safe to work on the live process with high temperature, high pressure, high speed, humid and super noisy conditions.
I was wondering if we can connect dual element Thermocouple in parallel so that if one fails other keep the measurement healthy by that we can avoid the costly shutdown, emergency maintenance at unsafe conditions and odd hour maintenance?
I am sure there were enough amount of R&D and thoughts went through on this topic but at the end user level there is no application whereby we use parallel thermocouple for redundancy purpose. I really wonder what stops this parallel connection in process plants? is it something to do with reliability? or is it something to do with impedance of measurement loop ? or is it something to do with high current with the 2 thermocouple ?
Any idea how the exhaust thermocouple (EGT) connected in the jet engines? I suppose one Thermocouple failure cannot trigger the emergency landing.
Appreciate if you can put in your thoughts, experience, and ideas!
Thermocouples are widely used in the temperature measurement of power plants, refineries, petrochemical and other oil & gas applications. There are umpteen number of temperature measurement loops which are very critical for the process and safety systems.
Say for instance if you use Thermocouple in a critical PID control loop the failure of Thermoscope could lead to control loop failure (I know that systems come with 2 out of 3 Thermocouple elements these days ; assume you have one dual element Thermocouple) or in the case of protection (safety) system the controller trigger protective action as a result of measurement failure.
Its well known that systems comes with fault tolerant measurement loops such as 2OO3 measurement loops in the modern instrumentation systems, even in those cases we have to simulate the other loops while doing the live maintenance on the faulty loops so as not to trigger one more loop faulty. Even with the 2OO3 redundant measurement loop, Process engineers feel uneasy when you have one measurement failure; unless you rectify the issue immediately your reliability dependence goes back to only one transmitter (NO I don’t think anyone have ever implemented 1 out of 3 logic). There are certain process systems whereby its not very safe to work on the live process with high temperature, high pressure, high speed, humid and super noisy conditions.
I was wondering if we can connect dual element Thermocouple in parallel so that if one fails other keep the measurement healthy by that we can avoid the costly shutdown, emergency maintenance at unsafe conditions and odd hour maintenance?
I am sure there were enough amount of R&D and thoughts went through on this topic but at the end user level there is no application whereby we use parallel thermocouple for redundancy purpose. I really wonder what stops this parallel connection in process plants? is it something to do with reliability? or is it something to do with impedance of measurement loop ? or is it something to do with high current with the 2 thermocouple ?
Any idea how the exhaust thermocouple (EGT) connected in the jet engines? I suppose one Thermocouple failure cannot trigger the emergency landing.
Appreciate if you can put in your thoughts, experience, and ideas!