From 1ca4e5cc2378ee51df5a181df80fa11210543fd6 Mon Sep 17 00:00:00 2001
From: appleb_m <martin.appleby@psi.ch+>
Date: Tue, 16 Jun 2026 12:09:00 +0200
Subject: [PATCH] Defining a bec device pv as a variable that can be called is
 significantly faster than calling motor.postion or motor.low_limit everytime.
 (~6 us compared to 200 ms)

---
 src/aare/daq/devices.py | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/aare/daq/devices.py b/src/aare/daq/devices.py
index b5280c4b..bfa463bf 100644
--- a/src/aare/daq/devices.py
+++ b/src/aare/daq/devices.py
@@ -40,8 +40,10 @@ class BeamlineDevices:
         self.__smargon = smargon.Smargon(beamline)
         self.exp_shutter = ExperimentalHutchShutter(beamline=self._beamline)
 
-        #only used at the moment to get hlm and llm from BEC
-        self.__dtz = self.bec_worker.dev.det_z
+        #faster to define the dtz object here than in functions and then use
+        self.__dtz_rbk = self.bec_worker.dev.det_z.position
+        self.__dtz_llm= self.bec_worker.dev.det_z.low_limit
+        self.__dtz_hlm= self.bec_worker.dev.det_z.high_limit
         self.dtz_mod = cfg_get('daq.detector_distance_limit_modifier', 1.0)
         #TODO convert epics pvs to BEC
         self.__sample_cam = epicsAD(f"{BEAMLINE}-ES-MS:")
@@ -263,20 +265,20 @@ class BeamlineDevices:
 # Detector Z
     @property
     def dtz(self) -> float:
-        return self.bec_worker.get_det_z()
+        return self.__dtz_rbk
 
     @dtz.setter
     def dtz(self, value: float):
         self.set_dtz(value, wait=True)
 
     def set_dtz(self, value: float, /, wait: bool = True):
-        if value < self.__dtz.low_limit:
+        if value < self.__dtz_llm:
             #raise ValueError(f"Detector distance cannot be less than {self.detector_distance_minimum} mm")
-            logger.warning(f"Requested detector distance {value} is less than minimum: {self.__dtz.low_limit}, setting to minimum")
-            value = self.__dtz.low_limit + self.dtz_mod
-        if value > self.__dtz.high_limit:
-            logger.warning(f"Requested detector distance {value} is greater than maximum: {self.__dtz.high_limit}, setting to maximum")
-            value = self.__dtz.high_limit - self.dtz_mod
+            logger.warning(f"Requested detector distance {value} is less than minimum: {self.__dtz_llm}, setting to minimum")
+            value = self.__dtz_llm + self.dtz_mod
+        if value > self.__dtz_hlm:
+            logger.warning(f"Requested detector distance {value} is greater than maximum: {self.__dtz_hlm}, setting to maximum")
+            value = self.__dtz_hlm - self.dtz_mod
         if wait:
             status = self.bec_worker.det_z(value, timeout=60)
             return status
@@ -286,11 +288,11 @@ class BeamlineDevices:
 
     @property
     def dtz_low(self) -> float:
-        return self.__dtz.get("LLM")
+        return self.__dtz_llm
 
     @property
     def dtz_high(self) -> float:
-        return self.__dtz.get("HLM")
+        return self.__dtz_hlm
 
     @property
     def aerotech_pos(self) -> AerotechCoordinate: