Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question dated 2020-08-04

The sensing elements of differential pressure transmitters generally consist of either a single diaphragm or a diaphragm box assembly. The single diaphragm is easy to manufacture, while the diaphragm box can withstand unidirectional operating pressures. The operating pressure of differential pressure transmitters is often much higher than the differential pressure being measured, which gives them high sensitivity; however, they cannot tolerate unidirectional overloads. The sensing element in the vast majority of differential pressure transmitters is a diaphragm box assembly. This is because such assemblies exhibit excellent sensitivity and linearity within the range of differential pressures for which they are designed to operate. Even when the differential pressure exceeds this operating range, that is, in the case of one-way overload, the diaphragm does not get damaged and its performance is hardly affected – this is a characteristic of the diaphragm box structure. Since the diaphragm box is filled with silicone oil, in addition to transmitting pressure it also provides damping, resulting in a stable instrument output.

The sensing elements of differential pressure transmitters generally consist of either a single diaphragm or a diaphragm box assembly. The single diaphragm is easy to manufacture, while the diaphragm box can withstand unidirectional operating pressures. The operating pressure of differential pressure transmitters is often much higher than the differential pressure being measured, resulting in high sensitivity; however, they cannot tolerate unidirectional overloads. The sensing element in the vast majority of differential pressure transmitters is a diaphragm box assembly. This is because such assemblies exhibit excellent sensitivity and linearity within the range of differential pressures for which they are designed to operate. Even when the differential pressure exceeds this operating range, that is, in the case of one-way overload, the diaphragm does not get damaged and its performance is hardly affected – this is a characteristic of the diaphragm box structure. Since the diaphragm box is filled with silicone oil, in addition to transmitting pressure it also provides damping, resulting in a stable instrument output.

A single-diaphragm design has poor one-way pressure resistance and is prone to damage, while a diaphragm box design can avoid this problem.

The sensing elements of differential pressure transmitters generally consist of either a single diaphragm or a diaphragm box assembly. The single diaphragm is easy to manufacture, while the diaphragm box can withstand unidirectional operating pressures. The operating pressure of differential pressure transmitters is often much higher than the differential pressure being measured, which gives them high sensitivity; however, they cannot tolerate unidirectional overloads. The sensing element in the vast majority of differential pressure transmitters is a diaphragm box assembly. This is because such assemblies exhibit excellent sensitivity and linearity within the range of differential pressures for which they are designed to operate. Even when the differential pressure exceeds this operating range, that is, in the case of one-way overload, the diaphragm does not get damaged and its performance is hardly affected – this is a characteristic of the diaphragm box structure. Since the diaphragm box is filled with silicone oil, in addition to transmitting pressure it also provides damping, resulting in a stable instrument output.

The sensing elements of differential pressure transmitters generally consist of either a single diaphragm or a diaphragm box assembly. The single diaphragm is easy to manufacture and offers high sensitivity, but it cannot withstand one-way overloads. The sensing element in the vast majority of differential pressure transmitters is a diaphragm box assembly. This is because such assemblies exhibit excellent sensitivity and linearity within the specified differential pressure range; moreover, when the differential pressure exceeds this range, that is, in the case of one-way overload, the diaphragm does not get damaged and is hardly affected at all – this is a characteristic of the diaphragm box structure. Since the diaphragm box is filled with silicone oil, in addition to transmitting pressure it also provides damping, resulting in a stable instrument output.

Since diaphragm boxes can withstand unidirectional operating pressures, the operating pressure of differential pressure transmitters is often much higher than the differential pressure being measured. Due to careless operation or other abnormal conditions, the measuring element may inevitably be subjected to unidirectional operating pressures that are far above its measurement range. Although a single diaphragm is easy to manufacture and highly sensitive, it cannot withstand unidirectional overloads; therefore, diaphragm boxes are used in the vast majority of differential pressure transmitters. At the same time, within the operating differential pressure range, the diaphragm box assembly exhibits good sensitivity and linearity; when the differential pressure exceeds this range, its performance is only minimally affected.

Because the diaphragm box assembly exhibits excellent sensitivity and linearity within the operating differential pressure range; when the differential pressure exceeds this range, that is, in the case of one-way overload, the diaphragm box not only remains undamaged but also suffers very little impact； Since the diaphragm box is filled with silicone oil, it not only transmits pressure but also provides damping, resulting in a stable instrument output ； It can be seen from the above that a single diaphragm cannot withstand one-way overload; although it is easy to manufacture and highly sensitive, it is not suitable for use.

①The sensing elements of differential pressure transmitters generally come in two types: single-diaphragm and diaphragm box assemblies. The single-diaphragm type is easy to manufacture and has high sensitivity, but it cannot withstand one-way overloads. ②The sensing element in the vast majority of differential pressure transmitters is a diaphragm capsule assembly. This is because such assemblies exhibit excellent sensitivity and linearity within the range of differential pressures for which they are designed to operate. Even when the differential pressure exceeds this operating range, that is, in the case of one-way overload, the diaphragm capsule does not get damaged and its performance is hardly affected – this is a characteristic of the diaphragm capsule structure. ③Since the diaphragm box is filled with silicone oil, in addition to transmitting pressure it also provides damping, resulting in a stable instrument output.

The sensing elements of differential pressure transmitters generally fall into two categories: single-diaphragm and diaphragm-box assemblies. The single-diaphragm type is easy to manufacture, while the diaphragm-box type can withstand unidirectional operating pressures. Differential pressure transmitters operate at pressures that are often much higher than the differential pressure being measured; they offer high sensitivity, but they cannot tolerate unidirectional overloads. The sensing element in the vast majority of differential pressure transmitters is a diaphragm box assembly, as this type of assembly exhibits excellent sensitivity and linearity within the differential pressure range it operates in