Rosemount 3051DP vs. 3051CD: What’s the Actual Difference?
So, you’re looking at Rosemount 3051 pressure transmitters and your brain is going, “Wait, what is the difference between a Rosemount 3051DP and a Rosemount 3051CD?” It’s a super common question. They look almost identical, and the names are confusingly similar. But trust me, the difference is simple and super important. It all comes down to one key concept: what type of pressure they’re designed to measure.
In a nutshell, the Rosemount 3051DP is a Differential Pressure (DP) transmitter, while the Rosemount 3051CD is a Gauge Pressure (GP) transmitter. “CD” is actually part of an older naming convention from Rosemount that stands for “Compact, Gauge Pressure.” Let’s break that down in plain English.
The Core Concept: What Are You Measuring?
Think of it like this:
Gauge Pressure (3051CD): This is pressure relative to the atmospheric pressure around us right now. It’s what most pressure gauges you see show. For example, when you check the air pressure in your car tire, you’re measuring gauge pressure. The transmitter uses the atmospheric air as its reference point. The “C” in 3051C originally stood for “Compact” and the “D” for the specific model, which in this case is Gauge.
Differential Pressure (3051DP): This measures the difference in pressure between two separate points. It doesn’t care about atmospheric pressure. It has two inlet ports and its main job is to tell you the pressure drop between them. This is crucial for things like measuring flow, liquid level in closed tanks, or filter clogging.
Okay, But What Does That Actually Mean for You?
The internal design and how they connect to your process are the big giveaways.
The Rosemount 3051CD (Gauge Pressure)
Has One Process Connection: You’ll typically see a single port where you connect your pressure line. Internally, the other side of its sensor is vented to the atmosphere. It’s literally measuring your process pressure against the air in the room.
Common Jobs: Tank level (for open tanks vented to atmosphere), liquid pressure in a pipe, and general pressure monitoring where you want a reading relative to ambient air.
The Rosemount 3051DP (Differential Pressure)
Has Two Process Connections: This is the dead giveaway. It has a “High” and a “Low” pressure port. It takes both pressures, compares them, and gives you a reading based on the difference between those two points.
Common Jobs: This is the real workhorse. It’s famously used with orifice plates to calculate flow rate (the DP across the plate tells you the flow). It’s also perfect for measuring level in a closed tank by comparing the pressure at the bottom and the top.
Quick Comparison Table
| Feature | Rosemount 3051CD (Gauge) | Rosemount 3051DP (Differential) |
|---|---|---|
| Full Name | Gauge Pressure Transmitter | Differential Pressure Transmitter |
| Pressure Type | Measures against atmospheric pressure | Measures difference between two points |
| Number of Ports | One primary process connection | Two (High & Low side) |
| Best For | Tank level (open), pressure monitoring | Flow measurement, filter monitoring, tank level (closed) |
Which One Should You Choose? It’s Simple.
Choose the 3051CD (Gauge) if you need to know the pressure at a single point compared to the air pressure around the transmitter. Think: “What’s the pressure inside this pipe?”
Choose the 3051DP (Differential) if you need to know the difference in pressure between two points. Think: “Is the pressure before this filter higher than after it?” or “What is the flow rate in this line?”
While you can sometimes configure one to act like the other in certain situations (like using a DP transmitter for gauge pressure by leaving the low-side vented), it’s always best to use the right tool for the job from the start.
Hopefully, this clears up the confusion. Picking the right one saves you a huge headache later on