修改控流阀死区为800，优化切换目标流量时PID模式切换逻辑，优化open_loop.py的--help显示，修改模式切换观察周期为10，更新了README.md

flow_control.py

@@ -97,7 +97,7 @@ class FlowControlLoop:
         pid_near_error_target_ratio=0.05,
         pid_far_error_min_slm=12.0,
         pid_far_error_target_ratio=0.20,
-        pid_mode_switch_confirm_cycles=3,
+        pid_mode_switch_confirm_cycles=10,
         logger=None,
     ):
         if period_s <= 0:
@@ -212,7 +212,32 @@ class FlowControlLoop:
         target_changed = target != self.target_flow_slm
         self.target_flow_slm = target
         if target_changed:
-            self._apply_pid_mode("FAR", reason="目标流量切换")
+            self._pid_mode_confirm_count = 0
+            if self.last_flow_slm is None:
+                self._apply_pid_mode(
+                    "FAR",
+                    reason="目标流量切换且尚无有效流量",
+                )
+            else:
+                error_abs = abs(target - self.last_flow_slm)
+                near_threshold, _ = self._pid_error_thresholds(target)
+                if error_abs > near_threshold:
+                    self._apply_pid_mode(
+                        "FAR",
+                        reason=(
+                            f"目标流量切换后 |误差|={error_abs:.3f} SLM "
+                            f"> NEAR 阈值={near_threshold:.3f} SLM"
+                        ),
+                    )
+                else:
+                    self._log(
+                        "info",
+                        "目标流量切换后保持 PID %s 模式："
+                        "|误差|=%.3f SLM <= NEAR 阈值=%.3f SLM",
+                        self.pid_mode,
+                        error_abs,
+                        near_threshold,
+                    )
 
     def start(self, initial_opening=100.0):
         """复位状态并启动控制；默认从全开开度开始。"""
@@ -356,13 +381,8 @@ class FlowControlLoop:
     def _update_pid_mode(self, flow):
         """按误差滞回切换 FAR/NEAR；参数只在模式变化时更新一次。"""
         error_abs = abs(self.target_flow_slm - flow)
-        near_threshold = max(
-            self.pid_near_error_min_slm,
-            self.pid_near_error_target_ratio * self.target_flow_slm,
-        )
-        far_threshold = max(
-            self.pid_far_error_min_slm,
-            self.pid_far_error_target_ratio * self.target_flow_slm,
+        near_threshold, far_threshold = self._pid_error_thresholds(
+            self.target_flow_slm
         )
 
         if self.pid_mode == "FAR":
@@ -392,6 +412,17 @@ class FlowControlLoop:
             ),
         )
 
+    def _pid_error_thresholds(self, target):
+        near_threshold = max(
+            self.pid_near_error_min_slm,
+            self.pid_near_error_target_ratio * target,
+        )
+        far_threshold = max(
+            self.pid_far_error_min_slm,
+            self.pid_far_error_target_ratio * target,
+        )
+        return near_threshold, far_threshold
+
     def _apply_pid_mode(
         self,
         mode,