Excela FAQs


1.       What problem does the Excela solve?

There are advantages and disadvantages associated with the use of modern day transmitters and traditional electromechanical switches in a facility. From a maintenance standpoint, an operator could spend at least 10x the amount of time trying to maintain a switch compared to a transmitter. On the other hand, a transmitter could be costly and sometimes overkill for a simple application. There is a gap in the market for an affordable, easy to install, drop-in-upgrade instrumentation type for a facility’s aging mechanical switch infrastructure. The Excela was developed from the ground up to combine the benefits of the electromechanical switch (e.g., simplicity) and the transmitter (e.g., accuracy) at an affordable price point to solve these maintenance and upgrade cost challenges.

2.       What are the key benefits of the Excela?

  • Easy integration with PLC, DCS and I/O card (8 – 50 VDC input). This is achieved with Excela’s 2 wire power and signal patented design.
  • Precise control and performance. Programmable deadband can be adjusted up to 99% of sensor operating range and a switch accuracy of 0.5%.
  • Local visual indication of operational status. Red/Green LED indicator on LCD display to show normal versus alarm condition
  • Weatherproof versatility. Excela is NEMA 4X and IP66 certified for use in both outdoor and indoor applications.

3.       What applications can the Excela be used in?

The Excela electronic switch is intended for plant upgrade applications by replacing mechanical switches with the latest digital switch technology.  It utilizes the existing mechanical switch wiring and the connected discrete input power source. In most cases, Excela is a direct, drop-in replacement for existing mechanical pressure, differential pressure and temperature instrumentation, providing an easy and cost-effective way to upgrade instrumentation within a plant. Some of the popular applications include monitoring of pressure and temperature for alarm and emergency shutdown in systems like: lube oil, boiler and furnace feed pumps, cooling and chiller water injection pumps, compressors and many more.


4.       What sensor types are available with the Excela?

The Excela is currently available in pressure, differential pressure and temperature models. Available ranges as follows:

  • Pressure​ : -14.7 to 6000 psi; -1 to 413 bar
  • Differential Pressure​: 0 to 200 psid; 0 to 13 bar​
  • Temperature​ : -300 to 1000°F; -184 to 538°C

Specific models are listed in our technical brochure

5.       What is the minimum load requirement on the Excela electronic switch?

The Excela connects to the input side of a PLC, DCS or I/O card that has an input voltage of 8 to 50 VDC.  When connected to these devices, Excela uses the small amount of residual current present on the input side of these devices.  Since Excela is an electronic switch, there is a power requirement during start up. The minimum load requirement (i.e., current) needed to power up the unit when connected to a digital input is 2.7 mA (3.0mA at -40°F/-40°C)

6.       Is the Excela a loop powered device?

Excela is an electronic switch and can provide a switch trip point anywhere within the range. It  does not have the capability for a 4 – 20 milliamps proportional analog signal output.

7.      Can  I use the Excela to directly switch AC loads?

The current version of the Excela cannot be powered by or switch AC loads.  Our research shows that majority of applications use PLC’s or similar devices that have a 24VDC input.  The use of an interposing relay can be that bridge between Excela and the AC load. Please contact our “Ask an Expert” page on UE’s website ueonline.com for additional help.

8.       What kind of switch output do I get with the Excela?

The Excela electronic switch provides a single pole double throw (SPDT) output. The Excela provides wiring connections for both Normally Closed and Normally Open operations. The 3 wire terminal block inside the Excela enclosure matches the 3 terminals found on an SPDT switch.

9.       How do I wire to the Excela electronic switch?

The signal output of the Excela mimics that of a single pole double throw (SPDT) mechanical switch.

a. If you are replacing a mechanical switch, the easiest way to wire the Excela is to migrate the wires from the mechanical switch to the exact same terminals on the Excela unit. i.e., just duplicate the wiring from the mechanical switch on the Excela wiring terminals.

b. Otherwise, please refer to the below for what the programmable logic controller (PLC) detects when the Excela is connected to a PLC and determine your wiring configuartion:

      • When wiring Normally Open (NO) and Common (COM)
        • PLC sees open circuit below setpoint
        • PLC sees closed circuit above setpoint
      • When wiring Normally Close (NC) and Common (COM)
        • PLC sees closed circuit below setpoint
        • PLC sees open circuit above setpoint

c. Wiring for bench testing.  If you want to test and set the switch set-point prior to connecting it to your PLC, you can use a 24 VDC power supply to power the unit.  To do this make sure you connect one of your wires to the resistor that is provided with the unit for bench testing.  The resistor value is 1.8K ohms and will act as a load in the connected circuit.  If you do not use a load resistor, the unit will still power up, but will overheat and the internal thermal fuse will shut down the power down before its electronics gets damaged.

10.       What is the minimum deadband setting on the Excela electronic switch?

Excela allows you to adjust the Rise and Fall set points and the difference between the two is known as the switch dead band or differential.  Deadband value can be programmed up to 99% of the sensor operating range.

11.       Can the Excela be used for outdoor applications?

The Excela can be used in both indoor and outdoor applications in environments from -40°F (-40°C) to 160°F (71°C). The product is fully gasketed and carries the NEMA TYPE 4X and IP66 ratings.

12.   What certifications are available with the Excela?

Excela carries the cULus  certification making it approved for use in North America and other regions that accept a UL approval.  In addition UL, Excela also carries the CE marking for use in the European Economic Area (EEA).  It also carries the enclosure Type 4X and IP66 approvals. The product also complies with RoHS requirements.

13.   Are pressure and temperature sensors for the Excela field replaceable?

The temperature sensors are field replaceable but the pressure sensors are not.

  • For the temperature sensors, make sure the elements meet the same specifications as the ones provided by United Electric Controls. The RTD used for the Excela is a 100-ohm platinum 4-wire, DIN 0.00385. By selecting the correct replacement element, the Excela electronics will automatically recognize and calibrate with the new RTD sensor
  • For the pressure sensors, they are not field replaceable on Excela because the calibration data for the sensor is stored in the unit’s display module. If either of the components (sensor or module) are changed, the calibration data will not match and therefore create a large display error.

14.   Can I get other wetted materials besides stainless steel with the Excela?

The Excela pressure and temperature sensors are only available with 316L stainless steel wetted material.  If other materials are required, the possibility of adding a chemical seal is one option to consider. If you have a special application that requires unique connections, please contact Inside Sales at insidesales@ueonline.com or +1 617 923 6977 for additional information and guidance. The displacement on the Excela gage pressure and DP sensors are specified as 0.0005 cubic inches and in most cases is negligible, facilitating the addition of a chemical seal with relative ease.

Lead Time, Warranty, Order Information

15.   What is the lead time on the Excela?

Current lead time is 2 weeks for most pressure and temperature models. The Teflon extension model is slightly longer at 4 weeks after receipt of order. Please contact customer service at customerservice@ueonline.com or +1 617 923 6944 for details.

16.   What is the warranty period on the Excela?

36 months 

17.   How do I build a part number?

Refer to page 4 of the Excela technical brochure. Alternatively, you can use our product selector or contact our inside sales department for technical assistance at insidesales@ueonline.com or +1 617 923 6977

Device Maintenance

18.   What is the recommended maintenance procedure for the Excela electronic switch?

Most plants have their own internal procedures and guidelines for maintaining mechanical switches and transmitters.  Excela, being an electronic switch, has a much simpler maintenance procedure than a mechanical switch.  Excela has a digital display and set-points, and therefore during maintenance the recommendation would be to compare the display with an external calibrated gauge at various process points and make minor adjustments, if needed, through the offset and span features of the product. Please refer to page 11 of the installation manual for a list of manufacturer’s annual device checks to ensure optimal operation.

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