Pressure & Level Transmitter Cable Considerations

This article addresses common questions regarding the impact of cable length and voltage drop on the performance of our pressure & level transmitters.

Signal Type and Cable Length #

• 4-20mA Signal: For transmitters utilising a 4-20mA output signal, cable length is generally not a significant factor. The current loop is designed to be largely immune to voltage drops and resistance changes over typical cable lengths; even cables of up to 10 km will not affect the signal, provided the supply voltage is within the required sensor specification.
• Voltage Output (0.5-4.5V, 0-5V or 0-10V): If your transmitter uses a voltage output (e.g., 0.5-4.5V, 0-5V or 0-10V), the cable can influence accuracy. In these cases, we recommend calibrating the sensor with the cable connected to ensure the highest possible accuracy.

Calibration Explained #

Calibration doesn’t always mean adjusting the sensor’s output. It can also involve:

• Characterisation: Providing a calibration sheet that details the sensor’s output values at specific pressure points with the cable connected. This allows you to compensate for any cable-related effects in your data processing.

Supply Voltage and Performance #

A stable supply voltage is crucial for accurate sensor readings. Here’s what to consider:

• Minimum Voltage: Ensure that the supply voltage at the sensor remains above the minimum recommended voltage specified in the product datasheet.
• 4-20mA Operation: Our 4-20mA transmitters are designed to operate within a wide voltage range (9-32V DC). In a typical 12V DC system, the voltage drop across the cable is minimal (e.g., 0.1-0.2V) and unlikely to affect sensor performance. However, it’s always good practice to verify the voltage at the sensor.
• 0-10V Operation: Our 0-10V transmitters are designed to operate within a voltage range of 13-32V DC. In most cases, the voltage drop across the cable is minimal (e.g., 0.1-0.2V) and unlikely to affect sensor performance. However, it’s always good practice to verify the voltage at the sensor and allow for voltage drop.

Summary #

• 4-20mA Output: Cable length is generally not a concern.
• 0.5-4.5V, 0-5V or 0-10V Output: Consider calibrating the sensor with the cable connected for optimal accuracy.