diff --git a/saltax/instructions/generator.py b/saltax/instructions/generator.py
index f3183e5..1ae9331 100644
--- a/saltax/instructions/generator.py
+++ b/saltax/instructions/generator.py
@@ -12,6 +12,7 @@
 from tqdm import tqdm
 
 
+DEFAULT_EN_RANGE = (0.2, 15.0)  # in unit of keV
 SALT_TIME_INTERVAL = 2e7  # in unit of ns. The number should be way bigger then full drift time
 Z_RANGE = (-148.15, 0)  # in unit of cm
 R_RANGE = (0, 66.4)  # in unit of cm
@@ -165,7 +166,13 @@ def get_run_start_end(runid):
 
 
 def instr_file_name(
-    recoil, generator_name, mode, runid=None, rate=1e9 / SALT_TIME_INTERVAL, base_dir=BASE_DIR
+    recoil,
+    generator_name,
+    mode,
+    runid=None,
+    en_range=DEFAULT_EN_RANGE,
+    rate=1e9 / SALT_TIME_INTERVAL,
+    base_dir=BASE_DIR,
 ):
     """Generate the instruction file name based on the runid, recoil,
     generator_name, mode, and rate.
@@ -176,15 +183,19 @@ def instr_file_name(
     :param runid: run number in integer, default: None, which means we
         are loading data and instruction doesn't matter (strax lineage
         unaffected)
+    :param en_range: (en_min, en_max) in keV, default: DEFAULT_EN_RANGE as a placeholder
     :param rate: rate of events in Hz
     :param base_dir: base directory to save the instruction file,
         default: BASE_DIR
     :return: instruction file name
     """
+    if en_range is not None:
+        en_range = str(en_range[0]) + "_" + str(en_range[1])
+    else:
+        raise RuntimeError("en_range must be specified, and it can even be placeholder (0,0)")
+    # FIXME: this will shoot errors if we are on OSG rather than midway
     if runid is None:
         return "Data-loading only, no instruction file needed."
-
-    # FIXME: this will shoot errors if we are on OSG rather than midway
     else:
         if base_dir[-1] != "/":
             base_dir += "/"
@@ -199,6 +210,8 @@ def instr_file_name(
             + "-"
             + generator_name
             + "-"
+            + en_range
+            + "-"
             + mode
             + "-"
             + str(rate)
@@ -370,7 +383,7 @@ def generator_ambe(
 
 def generator_flat(
     runid,
-    en_range=(0.2, 15.0),
+    en_range=DEFAULT_EN_RANGE,
     recoil=8,
     n_tot=None,
     rate=1e9 / SALT_TIME_INTERVAL,