A MicroLogix 1100-based temperature logger remains a practical pattern for small thermal process skids that need local alarming, door interlocking, and CSV historian files without investing in a full PAC and SCADA stack. A representative bill of material uses the 1763-L16BBB controller, a 1762-IF4 analog input module for 4–20 mA transmitter loops, discrete expansion such as 1762-IQ16 or 1762-IQ8W6 for field contacts, and an AdvancedHMI (or similar .NET HMI) station that records CSV files because the MicroLogix 1100 has no native SD-card datalogging.

Scale the analog channel carefully. A common PT-100 transmitter spanning 0 to 100 °C over 4–20 mA produces raw counts in the neighborhood of 5529 to 27648 on the 1762-IF4 when configured for the appropriate data format. Use an SCP instruction to map that raw range onto engineering units 0.0 to 100.0 °C. Document the exact raw endpoints from a calibrated current source during commissioning; do not rely solely on textbook counts if the channel filter or data format bits differ in your I/O configuration.

Control and protection logic

Apply a rate-of-change limit in ladder so noise or a failing transmitter cannot slam the PID or alarm block with impossible steps. A simple per-scan clamp on the engineering-unit delta, or a rolling average before the alarm comparator, is enough for most batch tanks. Implement an overtemperature shutdown at 95 °C that drops heating enables and latches a fault requiring operator reset. Wire a door interlock on an N2 (or equivalent safety-related discrete input as defined by your risk assessment) so opening the enclosure or process door forces heaters and motion-permissive coils off regardless of the temperature PID output.

RawMin  := 5529    ; 4 mA endpoint example
RawMax  := 27648   ; 20 mA endpoint example
EngMin  := 0.0     ; deg C
EngMax  := 100.0   ; deg C
SCP(RawTemp, RawMin, RawMax, EngMin, EngMax, Temp_C)

; OT shutdown example threshold
if Temp_C >= 95.0 then OT_Shutdown := 1;

I/O allocation sketch

CSV logging without onboard SD

Because the MicroLogix 1100 cannot write an SD catalog locally, place logging in the HMI computer. AdvancedHMI can poll temperature, setpoint, OT shutdown state, and door interlock bits on a fixed interval and append CSV rows with timestamps. Keep the poll rate honest relative to the thermal time constant; half-second logging on a 500-gallon tank wastes disk without adding insight, while a 10-second interval may miss a fast heater runaway on a small block. Buffer files by day and include controller wall-clock or HMI PC time explicitly in the header so audits remain defensible.

Commissioning steps

1. Configure the 1762-IF4 channel for 4–20 mA and verify raw counts at 4 mA and 20 mA with a loop calibrator.
2. Enter SCP breakpoints (approximately 5529–27648 to 0–100 °C) and confirm mid-scale at 12 mA ≈ 50 °C.
3. Tune rate limiting so step tests do not chatter alarms.
4. Force temperature above 95 °C in a controlled test and confirm OT shutdown and latch behavior.
5. Open the door interlock on N2 and confirm heating outputs drop even if the temperature PID still requests heat.
6. Start AdvancedHMI CSV logging and validate file contents after thirty minutes of runtime.

Trend, alarm, and CSV checks before release

Incorrect IF4 data format bits produce raw ranges that make the textbook 5529–27648 mapping useless—always measure. Floating analog commons and missing 250 Ω burden assumptions on some transmitters create offset errors that look like SCP mistakes. HMI PCs that sleep or rotate USB-Ethernet dongles drop CSV gaps that operators blame on the PLC. Treat the logger as a system: controller scaling, discrete interlocks, and PC-side files must be validated together.

This architecture is intentionally modest, yet it delivers actionable thermal records for OEM skids and lab stands. When the application later outgrows MicroLogix memory or Ethernet connection limits, the same SCP ranges, OT threshold, and interlock philosophy port cleanly onto larger PLC & PAC systems while preserving operator familiarity with the CSV workflow.