In an increasingly safety-conscious environment, operators must protect their workers from the risk of explosion, where there is a known risk of their equipment becoming an ignition source.
Strictly regulated and enforced, IS applies wherever volatile or flammable substances, such as fuel, gas, or flammable dusts are present. With their potential to generate heat or sparking, hand-held radios use a number of methods to meet safety standards.
An Intrinsically safe portable radio designed to the standard can provide all the features and performance of a non-IS model. It will also have a number of enhancements and methods of protection to prevent explosions. These include:
- Full encapsulation of battery circuitry to prevent electrolyte ingress in the unlikely event of a cell rupture,
- use of anti-static material for the battery case,
- stored energy limitation in the radio circuit,
- prevention of internal sparking or overheating,
- component and conductor spacing to prevent short circuit caused by dust or atmospheric contamination. The IEC 60079-11 standard covers both the radio and battery and, if the battery is to be removable in a hazardous environment, it must be completely intrinsically safe in its own right. Not every radio brand has this degree of battery protection – check with your supplier.
Here’s how Intrinsically Safe protection is achieved
At the heart of the battery is a Lithium-Ion cell pack, with thermal cut-outs, and a cell condition monitor to prevent it being overcharged, or discharged too much. An IS charge contact isolator ensures that no energy can appear at the exposed charge contacts in normal use. Supply is fed to the radio via an IS current limiter and IS surge clamp. This will prevent arcing, should the battery terminal be shorted or the battery disconnected from the radio while it is in operation.
All IS circuit blocks are multiple-redundant, and the entire circuit is encapsulated, to exclude atmospheric contamination and electrolyte ingress, should a cell leak.
The radio power input also has an IS surge clamp. An IS power limiter divides power between the high-current transmitter power amplifier and an IS step-down voltage regulator that supplies the rest of the radio. All IS blocks are multiply-redundant.
The transmit power limiter ensures that the transmitted RF power cannot exceed the value specified in the standard for the particular rated Gas Group. The RF output is via an IS transmit/receive switch with redundancy to protect the receiver in the event of switch failure.
The IS step-down voltage regulator has two main outputs. The first is for the processor and receiver and, because it is limited to very low power, the complex circuits it supplies use standard printed circuit rules without the risk of hot-spots. The second regulator output is limited in current to a level appropriate to the audio amplifier and loudspeaker requirements. This limiter also has redundancy and the audio amplifier is strictly rated to ensure that speaker power is within the limit for the rated Gas Group.
For information about Intrinsically Safe portables from Tait you can read the press release on the website, or read the TP8100 IS Specification sheet for information regarding FM-approval for IS radio models.
This article is taken from Connection Magazine, Issue 5. Connection is a collection of educational and thought-leading articles focusing on critical communications, wireless and radio technology.
Share your views, comments and suggestions in the Tait Connection Magazine LinkedIn group.