JNTU B.Tech III INTRODUCTION TO INSTRUMENTATION Previous Question Paper (August/September - 2021 - R18)

The dual slope integrating type digital voltmeter operates by converting an input voltage into a time period, which is then measured by a digital counter. The process consists of two phases: the integration phase and the de-integration phase.

1. Integration Phase: The unknown input voltage (V_in) is applied to an integrator for a fixed time interval (T₁), determined by a counter. The output of the integrator rises linearly to a value proportional to the input voltage.

2. De-integration Phase: After T₁, the input is disconnected and a known reference voltage (-V_ref) of opposite polarity is applied. The integrator output ramps down linearly until it reaches zero. The time taken for this (T₂) is directly proportional to the magnitude of the input voltage.

The relationship is given by: V_in = V_ref × (T₂ / T₁). Since T₁ and V_ref are constant, the counter reading (T₂) provides a direct digital representation of V_in. This technique is highly accurate and inherently immune to noise and component variations.

Traditional programming relies on writing lines of code where the logic is defined by syntax and sequence, making it powerful for complex algorithms but prone to syntax errors. Graphical programming, such as LabVIEW, uses a visual interface where icons representing functions are connected by wires to represent data flow. This allows for faster development and easier integration with hardware instruments, as the visual layout inherently represents the physical measurement system.