Honeywell HC900 - Figure 17 - Sample Controlled Start-Up Configuration; Figure 18

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Design and Implementation of HC900 Control System - HC900 Safety configurations

50 HC900 Process & Safety Controller Safety Manual Revision 1.9

01/14

Figure 17 – Sample controlled start-up configuration

Module Replacement

DO-V and AO-V use an input module to verify the output’s value. Failure of the input module will cause the

FBFAIL pin the “ON” state; however the output of the block unless configured otherwise with logic will maintain

the output value without verification. Caution: configuration considerations must be taken by the user

configuration to prevent a verify fail and resulting failsafe action when repairing the failed input module.

Figure 18 – Sample VFAIL qualification

Figure18 illustrates a means to prevent VFAIL from turning on immediately after the input module is

replaced. FBFAIL driving high is latched by LTCH102 which when ANDed with an inverted input to

AND103 prevents the qualified VFAIL signal, VFAIL_Q, from driving ON. This configuration

enhancement allows the user to replace the failed input module without causing a VFAIL trip since the

module will be restarted automatically prior to reconnecting the field connections. The user would

subsequently re-enable VFAIL when it is LOW by toggling FB-RSTRT ON then OFF thus clearing the

Honeywell HC900 - Figure 17 - Sample Controlled Start-Up Configuration; Figure 18 - Sample VFAIL Qualification