---
title: "Closed loop MBI system"
subject: "Instrumentation II"
chapter: 1
key: "semester_5/instrumentation_ii:closed-loop-mbi-define"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/closed-loop-mbi-define
site: BCT Engineering
---

# Closed loop MBI system

Instrumentation II · Chapter 1: Microprocessor Based Instrumentation System

- Asked in: 2072 Chaitra, 1 marks; 2075 Chaitra, 2 marks (asked 2 times)
- Video: [Instrumentation-II || Open loop and closed loop microprocessor based system](https://www.youtube.com/watch?v=xeNjJ5OuYc8) — IOE
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/closed-loop-mbi-define
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-1

## Question

What do you understand by a closed loop MBI system?

## Short answer

A closed-loop microprocessor-based system feeds back the measured output through a sensor and ADC, compares it with the set value, and adjusts the actuator via DAC or output port to maintain the desired condition. For example, an oven temperature controller switches the heater based on sensed temperature to hold 200°C.

## Answer

A **closed loop MBI system** is a microprocessor based system in which the output (controlled variable) is continuously measured by a sensor, converted to digital form by an ADC and fed back to the microprocessor. The microprocessor compares it with the set value, computes the error, and drives the actuator through a DAC or output port so that the error becomes minimum. Example: a microprocessor controlled oven that keeps temperature at 200 deg C by switching the heater according to the sensed temperature.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In a closed loop MBI system, what is fed back to the microprocessor?
   A. Only the set value
   B. The sensed output (controlled variable) digitised by an ADC
   C. The program memory contents
   D. The clock signal
   Answer: B. The output is sensed, converted by the ADC and compared with the set value. (Key point: Definition)

2. What does the microprocessor do with the fed-back value?
   A. Ignores it and outputs a fixed value
   B. Stores it without comparing
   C. Compares it with the set value, computes the error and drives the actuator to minimise it
   D. Sends it directly to the sensor
   Answer: C. Error computation and correction is the purpose of the loop. (Key point: Error action)

3. Which is an example of closed loop MBI?
   A. An oven keeping 200 deg C by switching the heater according to sensed temperature
   B. A heater switched ON for a fixed time
   C. A traffic light on timer
   D. A stepper motor given step pulses without sensor
   Answer: A. The oven uses temperature feedback to switch the heater. (Key point: Example)

## Related in Instrumentation II

- [MBI features; open vs closed loop compared](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-features-open-closed) — Instrumentation II, chapter 1
- [Rationale for microprocessor; open-loop MBI; DMA](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Arationale-open-loop-dma) — Instrumentation II, chapter 1
- [Case study: revamping MBI system for CEO](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-ceo-revamp) — Instrumentation II, chapter 10
- [Open loop vs closed loop instrumentation](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aopen-closed-loop) — Instrumentation II, chapter 1, asked 2×
- [MBI block diagram, advantages and DMA](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-block-advantages-dma) — Instrumentation II, chapter 1
- [MBI block diagram and advantages in industry](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-block-advantages) — Instrumentation II, chapter 1

## Related in other subjects

- [Traffic light system of Kathmandu: open or closed loop](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Atraffic-light-justify) — Control Systems, chapter 1
- [Define control system and closed loop block roles](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Adefine-cs-bd-role) — Control Systems, chapter 1, asked 5×
- [Closed loop control system block diagram explained](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Awhat-is-cs-bd-closed-loop) — Control Systems, chapter 1, asked 4×
- [Steps to design closed loop control system](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aclosed-loop-design-steps) — Embedded System, chapter 7