Watlow Power Series Rev H - Manual (Page 23)

Chapter Five
Control Methods and Features
F e a t u r e s , C h a p t e r 5 Wa t l o w P o w e r S e r i e s ■ 5 . 1
5
Zero cross (also known as burst firing) provides even
output power with the lowest level of noise genera-
tion (RFI). Zero cross is the preferred method for
controlling a resistive load.
The controller determines when the ac sine wave
crosses the 0-volts point, then switches the load,
minimizing RFI.
Zero cross control is available for all Power Series
configurations.
Soft start and current limiting are not available
with zero cross control.
Setup Page:
• Enter the Setup Page by holding ± ¬ for 3 seconds.
• When the display reads [algo], press ® until [`Off]
[`set]
[Algo]
is displayed. Press У О to select [`ftb] fixed time
base, zero cross or [Urtb] variable time base, zero
cross.
Figure 5.1a — Zero cross switching.
SCR Switch On/Off Points
+
0
-
Fixed Time Base - Zero Cross
In the fixed time base control method, the selected
percentage power level output is generated over a
fixed time period (i.e. a fixed number of cycles),
regardless of power level selected. Resolution of oper-
ator selectable power may be more precise than the
fixed time base allows. Selected power output level is
rounded to the closest possible power output value in
full cycles as necessary.
Line voltage compensation is not used in the fixed
time base control method.
Setup Page:
• Enter the Setup Page by holding ± ¬ for 2 seconds.
• When the display reads [algo], press ® until [`Off]
[`set]
[Algo]
is displayed. Press У О to select [`ftb] fixed time
base, zero cross.
• Press ® until[1seC] is displayed.
[`Ftb]
Press У О to select [1seC] or [4seC].
Figure 5.1b — 40% power, fixed time base, 60 Hz, 1 sec
time base.
24 Cycles ON 36 Cycles OFF 24 Cycles ON 36 Cycles OFF
Zero Cross