Tuning The Er1200; Deadband; Zero & Span - Tescom ER1200 Series Operation & Service Manual

TUNING THE ER1200

There are 5 adjustments located on the control
card. The initial factory pot settings are listed
in the following table.
FUNCTION
Gain
Stability (Integral)

Deadband

Zero
Span
Note: The counter-clockwise end point from
which to start turning the pots is found by
rotating the pot counter-clockwise 25 turns.
• The easiest method for calibrating and
tuning the system is to use a volt meter to
monitor the setpoint and feedback voltages.
• Turn all the pots back to the factory settings.
• Apply a setpoint signal of at least 12.5%
(6 mAmps, 1.5 VDC if 1 - 5 VDC, or 1.25
VDC if 0 - 10 VDC).
• Rotate the Deadband pot until exhaust gas
can barely be felt escaping from the
exhaust port (see Figure 1, page 1) on the
base of the unit. Rotating the deadband pot
clockwise will decrease the deadband to the
point that the inlet and exhaust solenoid
valves will operate continuously. This will
result in a very accurate tracking response,
but obviously consumes gas. If the
deadband is increased by rotating the pot
counter-clockwise, pilot gas will be
conserved, but the system will not respond
to a change in setpoint or feedback until the
error signal is larger than the imposed
deadband voltage. This can result in drifting
of the feedback signal or no response to a
small change in setpoint signal.
Form # 1925 Rev. 4/06 TESCOM
CLOCKWISE
TURNS
11
5
7
18
13
6
• Apply a setpoint signal of about 2.5% (4.4
mAmps, 1.1 VDC if 1 - 5 VDC, or 0.25 VDC
if 0 - 10 VDC). Measure the feedback signal
and adjust the zero pot until the feedback
signal matches the setpoint signal. Rotating
the zero pot clockwise will increase the
feedback signal and a counter-clockwise
rotation will decrease the feedback signal.
Sufficient time should be given for the
system to respond between each
adjustment of the pots, especially if there is
a large control volume. Rotate the pots
slowly and observe the system reaction.
Zero Pot Rotation Effect
Signal (mA)
Figure 4: Zero Adjustment
• Apply a setpoint signal of about 95% (19.2
mAmps, 4.8 VDC if 1 - 5 VDC, or 9.5 VDC if
0 - 10 VDC). Measure the feedback signal
and adjust the span pot until the feedback
signal matches the setpoint signal. Again,
sufficient time should be given for the
system to respond between each
adjustment of the pots. Since the zero and
span adjustments interact with one another,
it is necessary to readjust the zero after
adjusting the span. Recheck the zero and
adjust it if the feedback signal does not
match the setpoint signal of 2.5%. Continue
to recheck zero and span until the feedback
signal and setpoint signal match at both the
low and high setpoint values.