Have you ever heard the terms bypass, inhibit, force, and override on a control instrument system? If maintenance is applied to a plant or plant in the form of preventive maintenance , there are times when we have to treat the system that is online or the term live process, where the system in factory is not stop. And sometimes we also have to do corrective maintenance or corrective maintenance on the system that is online or live process.
For example in calibration at pressure transmitter, we will give simulation pressure from hand pump to pressure transmitter in question. The pressure value is generally from 0% to 100%, the problem is, if the transmitter is related to the shutdown or alarm system, then the process will shutdown when the pressure is simulated if the effect of the transmitter is not override. There are other terms to name the override, ie bypass, inhibit, force and override so that instrument equipment can be fixed while the process is online or live process. let's discuss the four terms
Bypass is any form of modification of both software and hardware that if done will negate the ability of an equipment to work properly, this can affect the safety factor of a tool.
Example: Force I / O on DCS / PLC software, jumper on cable terminals on control panel, etc.
Prevent or disable the function of the sensor or output of a system either software or hardware but does not eliminate the measurement function of the tool in question.
Example: Inhibit on gas detector during maintenance, Deadly flame detector due to damage.
It is one of the features in software for control systems that manipulate the value or status of a tag / register / bit in order to retain a certain status / value regardless of actual logic conditions. Force can be a bypass because it can shut down the detection function of a device / sensor / actuator, so it can prevent the system from shutdown.
Example: A pressure switch will be calibrated during the online process system, then before calibration the value of the pressure switch in DCS in force becomes logic
'HIGH', so that when the pressure switch calibrated the system will still get input 'HIGH', no matter the actual conditions in the local.
Change / replace the output response of a sensor or system both software and hardware. Similar to Force, only override does not eliminate the detection capability of a sensor / system, only its output response is "barren" right
Example: An override level transmitter will still detect the level, but if the alarm setting is reached, there is no response / output action to the next system.