A field transmitter can be measuring perfectly, but that measurement is of limited use if nobody can see it, understand it or act when the process moves outside the required condition.

Consider a pressure transmitter installed on a water line. It may be sending a healthy 4 to 20 mA signal, but the operator does not want to read current in milliamps. The operator wants to see the actual pressure in bar.

The same situation appears with tank level, flow, pressure, temperature and many other industrial measurements.

This is where process indicators and process controllers become useful.

Multispan's process control range includes digital process indicators, process controllers, scanners, data loggers, flow totalizers, signal isolators, load cell indicators and jumbo displays. Its process indicator and controller family is designed around configurable industrial analog inputs, with additional options such as alarm outputs, sensor supply, retransmission and RS485 Modbus communication depending on the model.

The challenge is not finding an instrument with a display. The challenge is deciding what needs to happen after the process signal reaches the panel.

What Is a Process Indicator?

A process indicator receives an industrial signal and converts it into a value that an operator can understand.

For example:

Pressure Transmitter → 4 to 20 mA → Process Indicator → 0 to 10 bar displayed

The transmitter generates the electrical signal. The process indicator scales that signal into engineering units.

The same basic idea can be used for:

• Pressure
• Tank level
• Flow
• Temperature
• Analytical measurements
• Speed signals converted into an analog value
• Other compatible process variables

Multispan's PI Series process indicators accept common analog inputs including 4 to 20 mA DC, 0 to 20 mA DC and 0 to 10 V DC. The PI Series is available in several panel sizes, including PI-11, PI-21, PI-38 and PI-41 variants.

This makes the PI range useful when the main requirement is clear local indication of a process signal.

What Is a Process Controller?

A process controller goes one step further.

Instead of only displaying the process value, it can also provide outputs that allow the panel to react when the measured value reaches a configured condition.

For example, a tank level transmitter may send a 4 to 20 mA signal representing 0 to 5 metres.

A process controller can display the level and use relay outputs for functions such as:

• High level alarm
• Low level alarm
• Pump start or stop logic
• Annunciation
• Interlocking with another control circuit

Multispan's PIC-1102 is an example of this type of process controller. It accepts 4 to 20 mA, 0 to 20 mA and 0 to 10 V inputs, provides two relay outputs and includes a 24 V DC transmitter supply. Optional retransmission and RS485 Modbus functions are also available in the process controller family.

The important distinction is therefore simple:

Process indicator: primarily shows the measurement.

Process controller: shows the measurement and can also participate in alarm or control logic.

Indicator or Controller: Which One Do You Actually Need?

A more expensive or feature rich controller is not automatically the better choice.

Start with what the process needs.

Many buyers begin with the question, "Which model should I buy?"

A better first question is, "What must happen after the signal reaches the instrument?"

Start With the Input Signal

Before selecting any process indicator or controller, identify the signal coming from the field.

This is one of the most important selection points.

Common process signals include:

• 4 to 20 mA DC
• 0 to 20 mA DC
• 0 to 10 V DC

The Multispan PI-11, PI-21, PI-38 and PI-41 process indicators support these common analog signal types.

A pressure transmitter with 4 to 20 mA output therefore needs an indicator configured for current input.

A device providing 0 to 10 V output requires the correct voltage input configuration.

Never assume that every process indicator accepts every type of signal.

Why 4 to 20 mA Is Common in Process Monitoring

Many industrial transmitters convert the measured process variable into a standard 4 to 20 mA signal.

For example, a pressure transmitter may be configured as:

4 mA = 0 bar

20 mA = 10 bar

The process indicator receives the current and scales it so the operator sees pressure instead of milliamps.

The same principle can be used for level, flow and other variables.

This is one reason process indicators are versatile. The instrument does not necessarily need to know whether the original measurement is pressure or level. It needs to receive a compatible electrical signal and be scaled correctly.

Scaling the Display Is Just as Important as the Input

Connecting a 4 to 20 mA transmitter is only part of the job.

The indicator also needs to know what that signal represents.

Suppose a level transmitter is configured for a 0 to 6 metre tank.

The display should be scaled so:

4 mA = 0.0 m

20 mA = 6.0 m

Without correct scaling, the electrical signal may be healthy but the displayed process value can still be meaningless.

Multispan's PI Series provides configurable display scaling and selectable decimal resolution for its supported analog inputs.

When replacing an existing indicator, write down both the electrical input and the engineering range before removing the old unit.

When Do You Need Alarm Relay Outputs?

A process indicator tells the operator what is happening.

Sometimes that is enough.

Other applications need an automatic response.

Consider a pressure system where normal operation is below 8 bar. The plant may want a relay to operate when pressure rises above the selected limit.

Or consider a storage tank where the operator needs:

• High level alarm
• Low level alarm
• Pump protection
• Overflow warning

This is when a process controller with relay outputs becomes useful.

The Multispan PIC-1102 provides two relay outputs, allowing it to perform more than simple indication.

Before selecting relay outputs, define exactly what each relay should do.

Do not simply order "two relays" without knowing their purpose.

When Is Built-In Transmitter Supply Useful?

Many field transmitters require a DC supply to operate.

In a conventional panel, this may be provided by a separate industrial power supply.

Some process controllers provide an inbuilt transmitter supply, which can simplify certain installations.

The PIC-1102 includes a 24 V DC transmitter supply.

A typical arrangement may therefore look like:

Process Controller → 24 V Supply to Transmitter → 4 to 20 mA Signal Back to Controller

This can reduce the need for a separate supply in some applications.

However, always confirm transmitter voltage and current requirements before connecting it to an instrument's built in supply.

What Is Retransmission?

Sometimes the process value needs to be visible locally and also sent to another instrument.

For example:

Pressure Transmitter → Process Controller → Local Display

and at the same time:

Process Controller → PLC / Recorder / Another Indicator

An analog retransmission output allows the process value to be passed onward as another analog signal, depending on the instrument configuration.

Multispan lists optional analog retransmission within its process indicator and controller range.

Retransmission can be useful where the plant wants local visibility without losing the ability to send the measurement elsewhere.

Before selecting it, confirm the input required by the receiving equipment.

When Do You Need RS485 Modbus?

RS485 Modbus becomes relevant when the process instrument needs to communicate digitally with an automation system.

Typical connections include:

• PLC
• HMI
• SCADA
• Data acquisition system
• Central monitoring system

Multispan offers optional RS485 Modbus communication on selected process control instruments.

This can be useful when several measurements need to be collected centrally.

But not every process point needs communication.

If the instrument is only being used for local indication, paying for communication may add complexity without providing much benefit.

Plan the communication architecture before ordering the panel instruments.

Panel Size Matters More Than It Looks

Process indicators are available in different front dimensions because every panel does not have the same space or visibility requirement.

Multispan's process indicator family includes several common sizes. For example, PI-11 is 96 × 96 mm, PI-21 is 72 × 72 mm, PI-38 is approximately 48 × 96 mm, and PI-41 is 48 × 48 mm.

A larger display may be useful where operators need easier visibility.

A compact 48 × 48 mm indicator may be more practical in a crowded OEM panel.

For replacement applications, always confirm:

• Front dimensions
• Panel cutout
• Available depth
• Terminal clearance
• Viewing distance

Never replace a process indicator based on front size alone.

Where Signal Isolators Fit

A process indicator and a signal isolator perform different jobs.

The indicator makes the measurement visible.

The isolator is used when the analog signal needs electrical isolation, conditioning or distribution.

For example, the Multispan MI-431 is a DIN rail signal isolator designed for analog signal interfacing. Radical TechMart lists it with single or dual output options, high noise rejection, three way optical isolation and an inbuilt transmitter power supply.

An isolator becomes worth considering when:

• One field signal needs to feed multiple systems
• Ground potential differences create measurement problems
• Electrical noise affects the signal
• PLC and field circuits need additional isolation
• A transmitter needs an isolated signal interface

Do not confuse signal isolation with process indication. They solve different problems.

Practical Example 1: Pressure Monitoring

Suppose you have a pressure transmitter with:

• Range: 0 to 10 bar
• Output: 4 to 20 mA

The requirement is only to show pressure on the control panel.

A process indicator is likely enough.

The setup becomes:

Pressure Transmitter → 4 to 20 mA → Process Indicator → 0 to 10 bar display

There is no need to choose a controller with multiple relay outputs if the plant only wants local monitoring.

Practical Example 2: Tank Level With High and Low Alarms

Now consider a tank level application.

The transmitter provides:

• Range: 0 to 5 metres
• Output: 4 to 20 mA

The plant requires:

• Local level display
• Low level alarm
• High level alarm

In this case, a process controller with relay outputs becomes more appropriate than a display only indicator.

The control concept could be:

Level Transmitter → Process Controller → Local Display + High Alarm + Low Alarm

If the value must also go to SCADA, RS485 communication or retransmission can then become part of the selection.

Practical Example 3: Flow Monitoring With Central PLC

Imagine a flow transmitter connected to a local panel.

The operator wants to see the flow locally, while the central PLC must also receive the measurement.

Possible approaches include:

Flow Transmitter → Process Instrument → Local Display → Retransmission to PLC

or

Flow Transmitter → Process Instrument → RS485 Modbus → PLC

The final choice depends on the control system architecture and what signal the PLC is designed to receive.

This is why communication requirements should be decided before the instruments are purchased.

Common Applications

Multispan process indicators and controllers can be used in applications such as:

• Pressure monitoring
• Tank level indication
• Flow monitoring
• Water treatment plants
• Pump systems
• Utility panels
• Chemical process systems
• HVAC plants
• OEM machinery
• Process skids
• Pharmaceutical plants
• Food and beverage processing
• Industrial production panels
• General process automation

Multispan specifically lists its PI process indicators for pressure, level, flow, temperature, analytical transmitter measurements and analog signals associated with VFD based RPM monitoring.

Common Selection Mistakes

Quick Selection Checklist

Before selecting a Multispan process indicator or controller, confirm:

1. What process parameter needs to be displayed?
2. What signal comes from the field transmitter?
3. Is the input 4 to 20 mA, 0 to 20 mA or 0 to 10 V?
4. What engineering range should appear on the display?
5. What decimal resolution is required?
6. Is indication only required?
7. Are high or low alarms required?
8. How many relay outputs are needed?
9. Does the field transmitter need a 24 V supply?
10. Is analog retransmission required?
11. Is PLC or SCADA communication required?
12. Is RS485 Modbus required?
13. What panel size and cutout are available?
14. What instrument power supply is available?
15. Is signal isolation required?
16. Has the final model been checked against the manufacturer datasheet?

Which Multispan Process Instrument Should You Consider?

Multispan's broader process control family also includes scanners and data loggers, flow totalizers, load cell indicators and jumbo displays, so applications that go beyond a single process point may need a different instrument family.

Why Buy Multispan Process Instruments from Radical TechMart?

Radical TechMart lists Multispan process instrumentation alongside its wider industrial automation range. Its current Multispan listings include PI Series process indicators and MI Series signal isolators, among other process and automation products.

A useful inquiry should not simply say:

"Need process indicator."

Instead, provide:

• Process parameter
• Transmitter output signal
• Engineering display range
• Required alarm outputs
• Supply voltage
• Panel size
• Transmitter supply requirement
• Retransmission requirement
• PLC or SCADA communication requirement
• Existing model, if this is a replacement

These details make it much easier to identify the correct instrument before comparing model numbers.

At Radical TechMart, the useful approach is to start with the process signal and what needs to happen with that signal afterward.

Final Thoughts

Choosing a process indicator or controller becomes much easier when you stop thinking about the display first.

Start with the field signal.

Then ask what the operator needs to see.

After that, decide whether anything needs to happen when the process reaches a particular value.

If only local visibility is required, a process indicator may be sufficient.

If alarms, control outputs, transmitter supply, retransmission or automation system communication are required, move toward a suitable process controller configuration.

The correct instrument is not the one with the most functions.

It is the one that matches the signal, display requirement, control logic and system architecture without adding unnecessary complexity.

FAQs

1. What is a Multispan process indicator?

A Multispan process indicator is a panel instrument used to receive and display compatible industrial analog signals. The PI Series supports common inputs such as 4 to 20 mA, 0 to 20 mA and 0 to 10 V.

2. What is the difference between a process indicator and a process controller?

A process indicator primarily displays the measured value. A process controller can additionally provide relay outputs or other functions so that the panel can react to configured process conditions.

3. Can Multispan process indicators accept a 4 to 20 mA transmitter signal?

Yes. Multispan PI Series process indicators support 4 to 20 mA input along with other analog input options depending on the model.

4. Can a process indicator display pressure, level or flow?

Yes. If the pressure, level or flow transmitter provides a compatible analog output, the process indicator can scale the signal into the corresponding engineering value. Multispan lists pressure, level, flow and temperature among PI Series applications.

5. When should I use a process controller instead of an indicator?

Choose a process controller when you need more than display, such as high or low alarms, relay outputs, transmitter supply, retransmission or communication.

6. What is transmitter supply in a process controller?

Transmitter supply provides DC power for a compatible field transmitter. The Multispan PIC-1102 includes a 24 V DC transmitter supply.

7. Can Multispan process controllers communicate with PLC or SCADA?

Selected Multispan process control instruments provide optional RS485 Modbus communication for integration with compatible PLC, HMI or SCADA systems.

8. What is retransmission in a process indicator or controller?

Retransmission sends a corresponding analog representation of the measured value to another compatible instrument, recorder or control system.