【2026 Pressure Instruments】Comparison of differences between SH/T 3005 and HG/T 20507 regarding pressure instruments

SH/T 3005 places pressure instruments in Chapter 6, the 2016 edition. HG/T 20507 is placed in Chapter 5, 2014 edition. The secondary clauses correspond basically; the units and ranges can be found for both local meters and remote transmission meters. The difference starts with the specific values of the tier-3 provisions.

1. Units and ranges: The units used are Pa, kPa, and MPa. Measure the stable pressure; the normal operating pressure should fall within the range of 1/3 to 2/3 of the scale, with both readings being consistent. The difference lies in the layer of additional constraints. SH calculates the pulse pressure as 1/3 to 1/2 of the value, while the transmitter is rated at 60% to 80% of its calibration range; in addition, all pressure instruments are required to have over-range protection, and vacuum measuring instruments are required to have under-range protection. HG only states that it is in line with the standard series of finished products in terms of range; the value of 1/3 to 1/2 of the pulsating pressure is specified in the selection criteria, and the over-range protection is included among the requirements for selecting the pressure gauge, without being mentioned separately.

Why does SH place the protection requirements in the range section? Petroleum-based media often contain pulses and instantaneous shocks. Including over-range and vacuum low-range protection in the general provisions sets a minimum standard for all pressure instruments, eliminating the need to assess each instrument individually. HG is designed for a broader range of chemical processing applications, with protection requirements specified separately based on phenotype.

II. Local pressure gauges: The boundaries between different pressure ranges represent the key difference; both types are classified according to the operating pressure, with options including Bourdon tubes, diaphragm boxes, and vacuum gauges. The terms for the dividing point and the vacuum section are different.

SH uses 40 kPa as the one-sided boundary. For pressures of 40 kPa and above, a Bourdon tube pressure gauge, that is, a differential pressure gauge, should be used ； Choose a diaphragm gauge for pressures below 40 kPa. Further down, there are single-column rectangular diaphragm micromanometers with a range of −500~+500 Pa, and single-column Bourdon tube vacuum gauges with a range of −0.1~+0 MPa. HG doesn’t cut it this way. It uses the symmetric values of ±40 kPa as the range for the diaphragm chamber; for the positive pressure side, values above 40 kPa offer two options: a bellows pressure gauge or a Bourdon tube gauge. The vacuum range is expressed as –100 to 0 kPa.

The difference in pressure ranges translates into a selection range of 0–40 kPa positive pressure; in both cases, membrane gauge instruments are recommended. What truly diverges is the slightly negative pressure range of −40~0 kPa: HG falls under the category of diaphragm gauges, while on the SH side, it is covered by micromanometers and vacuum gauges in the range of −500~+500 Pa; for the intermediate range, a judgment based on the measurement scale is required. The range units for the vacuum section are also different: MPa is used for SH, while kPa is used for HG; however, the converted ranges are the same.

The two approaches for special media are the same. For corrosive, solid-containing, or viscous media, use diaphragm or membrane gauges; for vibrating environments, use vibration-resistant gauges. The SH series is more detailed: special gauges are used for acetylene, ammonia, and oxygen-containing media; an oxygen gauge is used for oxygen; an anti-sulfur gauge is used for sulfur-containing media. For water vapor and media at temperatures above 60°C, a condensation coil or condensation bend is also required.

In terms of precision, HG offers one additional level, at 2.5, which enables measurement of larger sizes. The two grades in the precision range form separate series: SH is of 0.5/0.2/0.1 grades, while HG is of 0.4/0.25/0.16 grades; the numbers are close but not identical. The standard sizes for the dial are φ100 and φ150. The auxiliary dials are categorized as follows: SH uses φ50, which is intended for pressure relief valves and electrical valve positioners ； For HG, use φ60. The difference in material quality is the most noticeable. SH specifies that the pressure-sensing elements should be made of 316SS at the minimum, while Inconel alloy is required for use in seawater environments; furthermore, it is necessary that they can withstand 1.3 times the full scale load without the use of any auxiliary equipment ； The copper content in the low-copper aluminum alloy used for the watch case is kept below 8%. HG uses relative diameter, which is selected based on the properties of the medium and must be no lower than that of the pipe material.

Why are the materials and diameters different? SH is designed for highly corrosive conditions in the petrochemical industry; it fixes the lower limit at 316SS, eliminating the need for individual calculations. HG has a wide range of applicable diameters; the trade-off is that one must perform the calculations themselves during design.

3. Remote Transmitters: Signal Formats and Application Scenarios The remote transmission part is similar to the main system. Mainly pressure transmitters and differential pressure transmitters; differential pressure is used for micro-pressure and negative pressure, while diaphragm-sealed types are used for crystalline and corrosive media.