Introduction Signal Conditioning Challenges
Many types of signal conditioning challenges face us with sensors available for monitoring processes of all types. This includes temperature, level, flow, pressure, position, light, and so on; the list of applications using signal conditioning is endless.
Any industry, heavy or light, from farming to power generation, will make use of signal conditioning products. Each industry will present its own set of problems and requirements.
Some applications require the comparison of signals and an output based upon the result. For example, the amount of oil consumed by a burner will be the difference between the input and output of flow and normally, complex controllers or PLCs do this. However, functionality advances in signal splitters and multi-channel conditioners now mean that the conditioning block itself can do some of this work.
Challenges
Although basic signal conditioning has been in use for many years, it still presents a challenge to the process engineer. Any system that needs to transmit analogue signals, representing engineering values, from a measurement point to a monitoring/control point, needs to consider several things. For example, the mismatch of inputs to outputs, or the environment in which the system is located.
The output signal type and level from process sensors need to match the input requirements for controllers or PLCs, or problems can occur. A sensor with a (0 to 10) mA output might need to be connected to a controller with a (0 to10) V input, or even a different mA range. Matching the signals is the primary requirement of any signal conditioner.
To avoid ground loops, which can cause signal errors, requires the isolation of equipment inputs/outputs on the same control loop.
Ranging and scaling signals where sensor outputs are not in the same engineering unit or engineering unit multiple, and potential re-ranging if process conditions change, are potential pitfalls. If the conditioning block can be easily re-configured to a new input setting, when the working parameters for a process change then this makes installation a lot easier. For example: a flow sensor representing (0 to 100) l/min is connected to a data-logger which needs an input representing (0 to 50) l/min, where both are using a (4 to 20) mA signal. How will the conditioning unit cope with the mismatch?
Integrity
Signal integrity is important too. A loss of signal or an incorrect reading may cause a control system to fail or run outside of limits. Many factors from inside and outside the control system can affect integrity. A robust system is therefore essential in maintaining signal fidelity because the physical ambient conditions, length of cable run, electrical interference, can all cause problems.
Isolation between sensors that may become live in a fault condition can be a safety concern in some applications. For some engineers, a conditioner with a suitable rating can be a major factor in choosing the correct unit.
If more than one conditioner is required, a single device that can fulfill all of the requirements. The downside to this is that such a device can be complex and expensive.
Interfaces
In addition, it is important that process engineers choose equipment that can be easily interfaced because, controllers, PLCs, building management systems, and displays need to be integrated, to work with each other in many different combinations.
This is why most sensors, or the transducer the sensor may connect to, will look to convert its particular engineering value into something that can be interfaced with the vast majority of control systems on the market, which, to be practical, normally accept only a limited number of inputs. The industry “standards” for analogue signal transmission are within the ranges of (0 to 20) mADC or +/- (0 to10) VDC.
Solutions
Flexibility in modern signal conditioning technology is helping the process engineer to reduce the number of units required. This is by designing them to be multi-purpose, easy and quick to commission. The correct choice of signal conditioning device can solve many of the problems presented to the process engineer.
Status Instruments’ rail mounted SEM1700 range of single and dual channel conditioning and splitter products: designed to overcome many of the common issues associated with signal conditioning.
User-flexibility in the field is achieved through power supply, isolation and configuration. A worldwide power supply operating from 24 VDC all the way up to mains voltage. 3k75 V isolation between inputs and outputs. A wide range of input and output configuration.
Process engineers can use the dual channel device in two modes, simple and advanced. Simple – consider the basic features of a signal conditioner/splitter. Advanced – the functionality offers: user non lin, signal damping, system diagnostic tool, and other options, including recording, are available. Use FOC software and a standard USB lead to achieve set up.
