Honeywell STF724 vs. STF72F: What’s the Difference and Which One Should You Choose?
If you’re working in process control, especially in industries like chemical processing or hydrocarbons, you’ve likely come across Honeywell’s SmartLine ST700 series of flange-mounted pressure transmitters. Two models that often cause confusion are the Honeywell STF724 and the Honeywell STF72F. At first glance, they seem very similar—both handle comparable pressure ranges and share many high-end features. But they are not the same. The main difference lies in their physical installation design and process connection type. Understanding this distinction is crucial for selecting the right one for your application to ensure optimal performance, safety, and ease of installation.
A Quick Introduction to Honeywell’s SmartLine Transmitters
Before we dive into the differences, let’s set the stage. Honeywell’s SmartLine transmitters are known for their high accuracy, reliability, and robustness. They are workhorses in demanding applications like natural gas custody transfer, energy balance calculations, and measuring levels in pressurized and non-pressurized vessels35. They boast impressive features like:
Excellent Stability: As low as 0.02% of URL per year, which helps maintain accuracy over time and reduces the need for frequent recalibration24.
Wide Rangeability: A impressive 100:1 turndown ratio, offering great flexibility in adjusting the measuring range to your specific needs34.
Fast Response Time: As quick as 90-100 milliseconds, allowing them to catch rapid process changes34.
Side-by-Side: STF724 vs. STF72F
Now, let’s get to the heart of the matter. Here’s a breakdown of how these two models compare.
| Feature | Honeywell STF724 | Honeywell STF72F |
|---|---|---|
| Key Differentiator | Remote Seals & Process Interface | Direct Flange Mount |
| Process Connection | Uses a “process clamp” (e.g., 1/4″ or 1/2″ NPT with an adapter) or can be mounted on a 2″, 3″, or 4″ ANSI/DIN flange1. | Features a direct, fixed flange mount (e.g., 2″ or 3″ ANSI Class 150 flange)1. |
| General Application | More flexible installation options; can be configured for different connection needs. | Simplified, direct mounting to a vessel flange. |
| URL (Upper Range Limit) | 100 kPa24 | 100 kPa24 |
| LRL (Lower Range Limit) | -100 kPa24 | -100 kPa24 |
| Minimum Span | 1 kPa24 | 1 kPa24 |
| Reference Accuracy | ±0.05% of span2 | ±0.05% of span2 |
| Stability | 0.02% of URL per year2 | 0.02% of URL per year2 |
Diving Deeper into the Key Differences
The table shows that their core performance specs are identical. The real-world choice comes down to installation and your tank’s connection.
1. Physical Design and Mounting (The Biggest Difference!)
The STF724 is designed with a more versatile process interface system. It often uses a remote seal (or “insertion length” mentioned in specs1) connected via a process clamp and a capillary tube. This allows it to be mounted on larger ANSI or DIN flanges (like 2″, 3″, or 4″)1. Think of it as a more adaptable solution.
The STF72F, on the other hand, is a direct flange-mount transmitter. It typically has a fixed, smaller flange (like a 2″ or 3″ ANSI Class 150 flange)1 that bolts directly onto a matching flange on your tank or vessel. Its design is generally more compact and streamlined for this specific purpose.
2. Application Nuances
The STF724‘s design, with its potential for remote seals, can be beneficial for applications where you need to isolate the transmitter from extreme process temperatures or to use different diaphragm materials for compatibility with aggressive media13.
The STF72F offers a simpler, often more cost-effective solution when your vessel already has a compatible flange and a direct mount is sufficient. Its compactness can be an advantage in spaces with tight clearance.
3. Weight
There’s a subtle clue in the specifications about their physical difference. Documents indicate that models like the STF72F (with a direct flange) with an aluminum housing weigh between 6.4 – 8.7 kg, while the STF724 weighs between 8.2 – 14.5 kg1. This generally suggests the STF724’s configuration can be more substantial or complex.
Which One Should You Choose? STF724 or STF72F?
Here’s a simple guide to help you decide:
Choose the Honeywell STF724 if:
You need a flexible connection to your tank or process line.
You are working with larger flange sizes (e.g., 4″ ANSI or DN100 PN40).
Your application might require remote seals to protect the transmitter from high heat or corrosive chemicals.
Your existing setup uses a clamp and capillary system.
Choose the Honeywell STF72F if:
You have a vessel with a standard 2″ or 3″ ANSI flange ready for a direct mount.
You want a simpler, more straightforward installation without extra adapters or components.
Space is a consideration, and a more compact transmitter profile is beneficial.
Your process conditions are within the standard range for direct mounting.
Beyond the Model Number: Other Options to Consider
Remember, both models are part of the versatile SmartLine family. When ordering, you’ll also need to specify options like:
Diaphragm Material: 316L SS, Hastelloy C-276, or Monel 400 for compatibility with your process fluid1.
Fill Fluid: Silicone oil (DC200), fluorocarbon oil (CTFE), or others, depending on your operating temperature range1.
Electrical Connections: Choose from 4-20 mA HART, FOUNDATION™ Fieldbus, or Honeywell’s Digital Enhanced (DE) protocol46.
Display: Local alphanumeric display for troubleshooting and on-site readings.
The Bottom Line
So, what is the difference between Honeywell STF724 and STF72F? While they are performance twins in terms of accuracy and range, they are fraternal twins in design. The STF724 offers more flexibility in how it connects to the process, often through remote seals, while the STF72F is a straightforward, direct flange-mount unit.
Your choice isn’t about which one is “better,” but which one is right for your specific tank connection and application need. Always double-check your vessel’s flange specification and your process requirements before making the final call. When in doubt, consulting with a Honeywell expert or your supplier can ensure you get the perfect transmitter for the job.