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Building Technologies Basic documentation LMV37.4... CC1P7546en
12 Fan control 17.12.2018
12.15 Trim function
The trim function enables the specified speed of the fuel-air ratio control curve to be
changed in adjustable limits via 4
…20 mA input. The residual oxygen content of the flue
gas or the supply air temperature can be used for determining the current setting.
Depending on the setting, the trimming can be activated from ignition or only in
operation, between low-fire and high-fire, after an adjustable wait time has elapsed. No
trimming of the fan speed takes place during the curve setting.
The restriction of the trimming range must be selected so that no unsafe state can occur
in the application under any environmental conditions. The LMV37.4 also has various
options for ensuring that the trim function or the components involved in the trim function
run correctly (see chapter Optional internal checks / chapter Optional external checks).
Invalid output specification during trim function with LMV37.4.520A1
Note!
The LMV37.4 does not have any OPEN / CLOSED load controller inputs if the
switching back to pilot function (parameter 191) is activated.
When the trim function is activated, the output specification via the analog input also
no longer applies, which, in this case, only leaves the specification from the building
automation via Modbus as the lowest priority load controller source.
To protect the LMV37.4 from an invalid output specification (error code C: 60) in this
constellation after switching on or after a fuel change, a valid Modbus standard output
must be defined if the building automation is interrupted (Modbus parameter 148;
presetting is invalid).
No. Parameter
148
Predefined output in the event of communication breakdown with building
automation
Setting values:
For modulating operation, the setting range is as follows:
0…19.9 = burner off
20…100 = 20…100% burner output (20 = low-fire position)
For multistage operation, use the following settings:
0 = burner OFF
P1...P3 = stage 1...stage 3
Invalid = no output predefined by the building automation system in the event
of communication breakdown
Default setting: Invalid
Note!
A detailed description of parameters 148 and 149 can be found in the chapter Output
specification via building automation.
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