In industrial measurement, transmitter zero point and zero migration are fundamental concepts that ensure measurement accuracy. For pressure and differential pressure transmitters, understanding zero definition and distinguishing between different types of zero migration can effectively prevent measurement errors and ensure production data accuracy.
Today, we’ll break down the core concepts of zero point and zero migration using plain language and complete formulas. Whether it’s pressure transmitters or differential pressure transmitters, their working principle is based on measuring pressure differences between two sides. Zero point and zero migration essentially solve the “pressure balance” problem.
01 Core Definitions: Zero Point & Zero Migration
Zero Point
The zero point is the reference state where the transmitter measures zero differential pressure. Modern transmitters achieve ±0.075% ~ ±0.2% accuracy through optimized PCB layout and algorithms, while significantly reducing costs.
Zero Migration
When a transmitter’s two pressure-sensing diaphragms are connected to the atmosphere, the pressures on both ends are not equal—the differential pressure is not zero. We define this differential pressure value as the transmitter’s “new zero point.” This adjustment process is called zero migration.
Simple understanding: Through manual adjustment, a non-zero pressure difference state becomes the device’s “new zero point” to ensure accurate measurement.
👉 Key Point: Based on the pressure difference after the transmitter is pressurized, zero migration is divided into three types: zero migration, positive migration, and negative migration. Each corresponds to different installation scenarios and formula derivations.
02 Zero Migration: Balanced State Without Migration
Core characteristic: The pressures on both ends of the transmitter are equal, the differential pressure is zero, and no migration operation is required.
As shown in the figure (transmitter installed horizontally with the pressure tapping point, container medium at full level):
Let:
- ρ = medium density
- g = gravitational acceleration
- h₁ = height from high-pressure side tapping point to medium liquid level
- h₂ = height from low-pressure side tapping point to medium liquid level
Pressure Difference Formula Derivation:
ΔP = ρgh₁ - ρgh₂ = ρg(h₁ - h₂)
In the zero migration scenario, since the transmitter is installed horizontally with the tapping point, h₁ = h₂, therefore:
ΔP = ρg(h₁ - h₂) = ρg × 0 = 0
That is, the pressures on both ends of the transmitter are equal, the differential pressure is zero. At this time, no zero migration is required, and the device can directly use the current state as the zero point for measurement.
03 Positive Migration: Migration When Pressure Difference is Negative
Core characteristic: The pressures on both ends of the transmitter are not equal, the differential pressure is less than zero, and positive migration is required to adjust the zero point.
The transmitter is installed below the pressure tapping point, container medium at full level.
Pressure Difference Formula Derivation:
ΔP = ρgh₁ - ρgh₂ = ρg(h₁ - h₂)
In the positive migration scenario, since the transmitter installation position is lower than the tapping point, h₁ < h₂, therefore:
ΔP = ρg(h₁ - h₂) < 0
That is, the pressures on both ends of the transmitter are not equal, the differential pressure is less than zero. At this time, positive zero migration is required. By adjusting the device zero point, the current negative pressure difference state becomes the new measurement benchmark to ensure subsequent measurement accuracy.
04 Negative Migration: Migration When Pressure Difference is Positive
Core characteristic: The pressures on both ends of the transmitter are not equal, the differential pressure is greater than zero, and negative migration is required to adjust the zero point.
The transmitter is installed above the pressure tapping point, container medium at full level.
Pressure Difference Formula Derivation:
ΔP = ρgh₁ - ρgh₂ = ρg(h₁ - h₂)
In the negative migration scenario, since the transmitter installation position is higher than the tapping point, h₁ > h₂, therefore:
ΔP = ρg(h₁ - h₂) > 0
That is, the pressures on both ends of the transmitter are not equal, the differential pressure is greater than zero. At this time, negative zero migration is required. Adjust the device zero point to match the current positive pressure difference state to avoid measurement errors.
05 Summary
เดอะ zero point is the transmitter’s natural zero benchmark (differential pressure is zero). Zero migration is the operation of establishing a new zero point through manual adjustment for scenarios where the “natural differential pressure is not zero.”
The core differences between the three types can be summarized as follows:
d>No zero migration required
| Migration Type | Core Characteristic | Installation Scenario | Pressure Difference Formula | Migration Operation |
|---|---|---|---|---|
| Zero Migration | ΔP = 0 (Equal pressure on both ends) | Transmitter installed horizontally with tapping point | ΔP = ρg(h₁ – h₂) = 0 (h₁ = h₂) | |
| Positive Migration | ΔP < 0 (Unequal pressure, negative difference) | Transmitter installed below tapping point | ΔP = ρg(h₁ – h₂) < 0 (h₁ < h₂) | Positive zero migration required to match negative pressure difference |
| Negative Migration | ΔP > 0 (Unequal pressure, positive difference) | Transmitter installed above tapping point | ΔP = ρg(h₁ – h₂) > 0 (h₁ > h₂) | Negative zero migration required to match positive pressure difference |
Mastering their formula derivations and scenario characteristics enables quick resolution of transmitter zero adjustment problems in the field.
Practical Application Tips
When to Use Each Migration Type:
✅ Zero Migration:
- Standard installation where transmitter is at same level as tapping point
- Open tank level measurement with transmitter at tank bottom
- Gas pressure measurement in pipelines
✅ Positive Migration:
- Transmitter installed below the process connection (common in steam applications)
- Wet leg level measurement with condensate pot
- Preventing transmitter from exposure to high temperatures
✅ Negative Migration:
- Transmitter installed above the process connection
- Dry leg level measurement with impulse line filled with gas
- Applications requiring transmitter to be elevated for accessibility
Key Considerations:
- Always verify: Check transmitter specifications for maximum migration range (typically ±URL or ±100% of span)
- Calibration: Perform zero migration adjustment before span calibration
- Documentation: Record migration values for future maintenance reference
- Safety: Ensure process is stable and safe before performing migration adjustments
Recommended Brands for Zero Migration Applications
For reliable zero migration performance in pressure and differential pressure measurement, we recommend the following industry-leading brands:
🏭 Pressure & Differential Pressure Transmitters
- เอนเดรส+เฮาเซอร์ (E+H) – Swiss precision, industry-standard for process automation
- โรสเมาท์ – Emerson’s flagship brand, widely used in oil & gas
- โยโกกาวะ – Japanese engineering excellence, superior stability
- ซีเมนส์ – German technology, integrated automation solutions
- เอเอสบี – Swiss-Swedish innovation, advanced diagnostics
- ฮันนี่เวลล์ – American reliability, extensive industry experience
🎛️ Control Valves & Final Control Elements
- ฟิชเชอร์ – Emerson’s premier valve brand, global leader in control valves
As an authorized distributor, we supply 100% original products from all these brands . Contact us for technical support, product selection, and competitive quotations.
