13
3
Operation
Correction is active. The controller remains in the base firing rate position until a control ena-
bling signal (terminal 4) is given. Once control is released, the VMS tracks the externally ap-
plied firing rate. A current signal proportional to the position of the fuel/air ratio control is
emitted as internal firing rate (not on VMS 5). The mode display goes out.
3.3
Range Limits
In the 1
st
pre-purge after ’Clear memory’, the VMS determines the maximum range of travel
for each control element and stores this automatically. If no ranges limits have yet been deter-
mined, the setting (in the case of constant outputs the feedback setting) in pre-purge stands
at 0 and 999 points respectively. At all further starts a check is made to see that these range
limits are correct. Should the limit switches be shifted or the frequency converter setting
changed after programming, the range limits must be re-entered.
If the range limits cannot be determined automatically, they can also be entered manually by
using parameters. If the VMS has no existing range limits, it automatically takes the top and
bottom point of the curve as the limit. It then does not go beyond this.
3.4
Internal Firing Rate
The internal firing rate is the firing rate value at which the fuel/air ratio control currently stands.
It therefore corresponds indirectly to the output of the burner.
The internal firing rate is displayed in addition to the external firing rate signal.
In the ’firing rate value’ position therefore both the external firing rate (left-hand) and the inter-
nal firing rate (right-hand) are displayed.
The value of the internal firing rate can be outputted via the monitor output, in order to connect
further units (e.g. O
2
trim, only on VMS 4). When connecting other units, it must be remem-
bered that the signal in itself is not error-proof.
3.5
Manual Mode
When switching over to ’firing rate value’ with the burner running the burner firing rate can be
set by the VMS. The firing rate value can then be adjusted with the channel 1 toggle switch.
The system follows this firing rate value in the fuel/air ratio control.
Operating a switch other than channel 1 causes the unit to exit manual mode again.
3.6
Parameter Settings
The person commissioning the unit can adjust various functions of the VMS by using param-
eters (e.g. post-purge time). The parameters are classified into various safety levels. With the
exception of the lowest safety level these are accessible only with a password. The parameter
settings can be undertaken both on the unit itself and by using a PC and Windows software.
3.7
Correction
The VMS has 2 correction inputs. An analog signal (0/4 … 20 mA) can be connected to these
for shifting the set curves (e.g. for O
2
correction or air temperature correction). The assign-
ment of the correction to the individual output channels and the mode of operation can be ad-
justed by parameters.
Summary of Contents for VMS Series
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