Transmitter Failure Mode Low or High

R

Thread Starter

Rico

Transmitters have an independent circuit which is designed to provide backup alarm output if the microprocessor hardware or sofware fails. The alarm level is user-selectable using the failure mode switch (output is driven either High or Low). My question is, what's the advantage of selecting 'Low' or 'High', does it matter either way? Is it advisable to drive the output to 'Low' say 3.75 mA, i.e. is low power means fail safe?
 
G
The transmitter fail mode is determined by process it is monitoring. If the transmitter in question fails one way or the other, what is the more conservative control system response as far as safety, equipment protection, revenue etc.

Greg Ponto
Lead Combustion Turbine Specialist
Elwood Operations
(815) 423-9883 x2232
Email: [email protected]
 
The transmitter fail mode is determined by process it is monitoring. If the transmitter in question fails one way or the other, what is the more conservative control system response as far as safety, equipment protection, revenue etc.

Greg Ponto
Lead Combustion Turbine Specialist
Elwood Operations
(815) 423-9883 x2232
Email: [email protected]
i have situation when transmitter become iop after overshoot level more than 106.25%, and control valve in DCS become manual from Auto control. And it effect to process boiler feed water due to control valve maintain in manual control mode. Any suggestion to prevent this control turn to manual after iop. DCS : centum VP yokogawa.
 
i have situation when transmitter become iop after overshoot level more than 106.25%, and control valve in DCS become manual from Auto control. And it effect to process boiler feed water due to control valve maintain in manual control mode. Any suggestion to prevent this control turn to manual after iop. DCS : centum VP yokogawa.
What is iop??
 
Input Open Status Alarm. Typically is in alarm status when the loop is open (wiring), if the input is above 106% or below -6%. You would want reject control to manual mode in the event that your input is IOP as your measurement device (transmitter) is incapable of sending a signal. In the case of drum level DP measurement as the PV to a boiler feedwater loop it's likely that either your reference or sensing impulse tubing has vapor bubbles that need to be bled out to restore the transmitter output between 4 to 20 mA and IOP Status would return to NR (Normal).
 
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