APCS the Signal Conditioning Specialists

Find a Product Input ⇒ Function ⇒ Output

Select products that measure dc input parameters and produce a standard process signal output or an alarm state.

dc Input Products

Process Signals

Process signals are a standardised range in an electrical signal that represent a measured value.

For example a signal of 0 to 10Vdc can represent;

  • 100 to 1000kg of butter
  • 0 to 100°C ambient temperature.

The signal is an analogue communication within a standardised range. Common process signals are 4..20mA, 1..5V, 0..20mA, 0..10V, 10..50mA, 0..10mA, 0..1V and 0..5V.


4-20mA Input

This will select both auxiliary powered and output loop powered modules.

In most case the APCS signal conditioning module will have the option of supplying the input loop current derived from the auxiliary supply or the loop powered output.

This means the drive voltage could either be coming from the APCS module or the 4-20mA input device.

4-20mA External Source or Input Sourced Concept

4-20mA External Source or Input Sourced Concept


Why 4 to 20mA?

The most popular process control signal still used today is 4 to 20mA. It has a number of advantages over zero based and voltage signals.

  • Live Zero Commencement of the scale at 4mA, clearly distinguishes between zero and failure conditions of the signal.
  • Loop Power Signal below 4mA can be utilised to provide power to a loop or signal powered type of transmitter.
  • Noise Immunity The signal information is contained in the 16mA swing (20 - 4). The receiving instrument has typically a low input resistance (10 to 250Ω) which will render the current signal highly immune to electrical interference.
  • Long Cable Length The signal produced by the sensor/transmitter remains constant up to a specified maximum load resistance, so that type and length of cabling used is of little consequence.
  • Safety The low drive voltage required, usually 12 to 24Vdc provides a very high degree of safety.
Auxiliary Powered Transmitter Concept

Auxiliary Powered Transmitter Concept

4-20mA Input Powered

The drive for the 4 to 20mA is derived from the input device.

This current 4mA = 0% of output to 20mA 100% of output also powers the APCS signal conditioning module.

4-20mA Loop Input Powered Concept

4-20mA Loop Input Powered Concept

dc A Input

Select products that accept 1Adc or more. For lower currents use the dc mA/V input selection.

The load current to be measured is wired in series with an internal shunt or passes through a Hall Effect Current Transformer.


Shunts Inputs

Some products have an internal wired in series with the load current.

The shunt is a low value accurate resistor. The voltage drop across the shunt is E = I × R.

An accurate millivolt amplifier is then used to create an accurate measurement.

External shunts can also be used with mV measurement products.

50A Shunt

50A Shunt


Hall Effect Inputs

The DCT247/8 has a top mounted hall effect CT with link selected ranges from 1A to 100A. For higher currents the DCT247/8 may be used with a range of external hall effect CT's.

The current conductor passes through a magnetically permeable core that concentrates the conductor's magnetic field. The Hall effect device is mounted in the core at a right angle to the concentrated magnetic field. When the energised Hall device is exposed to a magnetic field from the core, it produces a potential difference (voltage) that can be measured and amplified.

Hall Effect Sensor

Hall Effect Sensor

dc mA/V mA and V Input

This selects products that cover the common process signal inputs.

Common process signals include: 4..20mA, 1..5V, 0..20mA, 0..10V, 10..50mA, 0..10mA, 0..1V and 0..5V.


dc mV Input

This selects products that include a high gain precision amplifier that will scale the small input signal to a level stable for processing.

mV transmitters and isolators are used in a wide range of applications where the signal from the sensing probe needs amplification before use.