Compound Range Pressure Transmitters for Bidirectional +/- Pressure

Compound range pressure transmitters for measuring both vacuum and positive pressures with one device.

Compound range pressure transmitters offer a versatile solution for applications requiring the measurement of both sub-atmospheric (vacuum) and positive pressures through a single instrument. These devices are uniquely calibrated, typically with a 4-20mA output corresponding to the full negative-to-positive pressure span, but their design using a single sensing diaphragm means engineers must consider potential accuracy limitations, especially when the positive and negative pressure ranges are substantially different. With configurable symmetric or asymmetric bidirectional ranges, these transmitters are adaptable to diverse industrial and research settings, from HVAC and cleanroom monitoring to specialized process vessel and test chamber applications.

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Find out more about Compound Range Pressure Transmitters to determine which product options and capabilities will best meet your application requirements.

Compound range pressure transmitters are specialized instruments engineered for applications demanding the measurement of both positive (above atmospheric) and negative (vacuum or below atmospheric) pressures utilizing a single sensing element and process connection. The standard electrical output, typically 4-20mA, is precisely calibrated so that the 4mA signal corresponds to the most negative pressure value of the calibrated range, while the 20mA signal represents the most positive pressure value. This unified design simplifies installations in systems where pressure conditions can fluctuate between vacuum and positive pressures, such as in certain pumping applications, suction lines, or vapor recovery systems.

The core of these transmitters employs a single sensing diaphragm to detect deflections caused by both positive and negative pressures. While this integrated approach is space-efficient and cost-effective, it introduces inherent limitations regarding the achievable accuracy across widely disparate positive and negative pressure spans. Specifically, the ratio between the maximum positive pressure and the maximum negative pressure (vacuum) significantly influences the precision at the lower end of the overall range. For example, a compound range pressure transmitter calibrated for -1 bar to +10 bar, with a nominal accuracy of 0.25% of full span (FS), will have its accuracy for the vacuum portion (-1 bar) effectively reduced. This is because the 0.25% accuracy applies to the total span (11 bar in this case), meaning the potential error (0.0275 bar) becomes a much larger percentage of 2.75%, when considered against the smaller 1 bar vacuum segment. Design engineers and calibration technicians must carefully consider this characteristic when specifying transmitters for applications with critical low-pressure or vacuum accuracy requirements alongside much higher positive pressure capabilities, such as in certain test chambers or specialized chemical reactors.

Gauge reference pressure transmitters are commonly configured to create compound ranges. These can span from a full negative gauge pressure of approximately -1 bar (around -15 psi, representing near total vacuum relative to ambient) up to various positive pressures, such as +2 bar (+30 psi) or higher, depending on the specific model and sensing technology. For pressure ranges substantially below 1 bar (15 psi), compound range transmitters often feature bidirectionally symmetric spans, for instance, -500 to +500 mbar. Such symmetric ranges are frequently utilized in applications like HVAC systems for differential pressure monitoring across filters, cleanroom pressure balancing, or managing draft control in combustion chambers where slight positive or negative deviations from atmospheric pressure are critical. However, it is also entirely feasible to configure these transmitters with asymmetric bidirectional ranges, such as -200 mbar to +500 mbar. This flexibility allows for tailored solutions in scenarios where the expected negative pressure excursions are different in magnitude from the positive pressure excursions, for example, in certain types of leak detection equipment or process vessels that primarily operate under a slight vacuum but can experience moderate positive pressures.