Siemens LME7 Series Technical Instructions page 127

LME Series
Honeywell Modutrol IV with the LME75 (continued)
Sequence of Operation without Valve Proving
1. The LME75 is in standby. All valves are closed and all relays are de-energized. All relay
contacts are as shown in the electrical schematic. The Honeywell Modutrol IV motor
(hereafter referred to as mod motor) is at the low fire position.
2. The LME75 receives a call for heat. Output X2-09.1 is energized in phase 21 to drive the
mod motor to low fire. Since the mod motor is already at the low fire position, the low
fire proving switch is closed, and actuator feedback input X2-09.4 is energized.
3. Output X2-09.3 is energized in phase 24 to drive the mod motor to high fire. Relay CR-1
is energized. Normally open contact CR-1A closes, connecting terminals R and B on
0-135 Ohm mod motors or terminals F and - on 4-20 mA mod motors. This drives the
mod motor to the high fire position. Once the mod motor reaches the high fire position,
the high fire proving switch closes, and actuator feedback input X2-09.4 is energized.
Normally open contact CR-1B also closes, but this has no effect since main valve output
terminal X7-04.4 is de-energized during this phase.
4. The LME75 progresses to phase 22 and phase 30 (prepurge). During this time, output
X2-09.3 remains energized, keeping the mod motor at the high fire position. Actuator
feedback input X2-09.4 is required to remain energized during these phases, proving
that the mod motor is at the high fire position for the full length of the prepurge.
5. Output X2-09.3 de-energizes in phase 36, de-energizing relay CR-1. Contact CR-1A
opens, removing the connection that was keeping the mod motor to high fire. Since
normally open contact CR-2 remains open, the mod motor drives to the low fire
position. Output X2-09.2 is energized in phase 36. Once the mod motor reaches the
low fire position, the low fire proving switch closes, and actuator feedback input X2-09.4
is energized.
6. If the jumper for direct ignition is not installed, the LME75 progresses through phases
40, 42, and 44 without any change to the mod motor. During these phases, the LME75
lights off the pilot and establishes a flame signal. The mod motor remains at the low fire
position, and actuator feedback input X2-09.4 is required to remain energized during
these phases, proving that the mod motor is at the low fire position through the light-off
sequence.
SCC Inc. Page 5
Technical Instructions
Document No. LME-1000
Appendix A