Former of Intrinsically Safe Parameters of the FIPEKM-1 Type
Abstract Generated abstract
This paper describes the FIPEKM-1 intrinsically safe parameter shaper developed to allow standard electrical-contact pressure gauges to be used for signaling in explosive hydrogen atmospheres. The authors motivate the device as an alternative to specially explosion-protected gauges, outline the permissible contact currents and circuit constraints for intrinsic safety, and present a transistor relay circuit located outside the hazardous area and connected by a communication line to the gauge contacts. The device signals three preset pressure limits, operates with very low contact voltage and current, and was reported to have passed intrinsic safety tests at VOSTNII. It is also proposed for use with other two- or three-position signaling instruments when the line resistance is within specified limits.
Full Text
INTRINSICALLY SAFE PARAMETER SHAPER OF THE FIPEKM-1 TYPE
V. F. Anikin, A. I. Kutyavin
(Presented by the scientific seminar of the Faculty of Automation and Computer Engineering)
When electrical apparatus is operated in an explosive atmosphere, appropriate measures must be taken, in accordance with the “Rules for the Manufacture of Explosion-Protected Electrical Equipment,” to ensure explosion protection.
In the manufacture of electrical-contact pressure gauges for category 4 of group A (hydrogen mixture), a number of difficulties arise.
- The labor input of the work increases by a factor of 3.
- Scarce materials must be used. In addition, the weight of the pressure gauge increases by more than a factor of two.
The use of a pressure gauge in the standard, general-industrial version with a semiconductor shaper of intrinsically safe parameters gives a twofold saving.
To create an intrinsically safe shaper it is necessary to select quite definite circuit parameters, which depend on the explosion hazard of the premises [1]. Table 1 gives the permissible values of the current through the contacts in a hydrogen atmosphere as a function of the inductance in the circuit being opened and of the voltage across the open contacts, 6 V [1].
Table 1
| \(L\), permissible | gn | 0.0001 | 0.001 | 0.01 | 0.1 | 0.5 | 1.0 |
|---|---|---|---|---|---|---|---|
| \(I\), permissible | ma | 300 | 150 | 55 | 40 | 17 | — |
To meet these restrictions, the problem of using instruments with electrical-contact signaling in the usual version in an explosive environment reduces to creating a device whose actuation power is less than that permissible in the given environment.
The shaper is located in an explosion-safe environment and is connected to the instrument being serviced by a communication line. This is illustrated by the block diagram in Fig. 1.
On this principle, a shaper of intrinsically safe parameters of the FIPEKM-1 type was designed and manufactured for an electrical-contact pressure gauge of the EKM type. Its schematic diagram is shown in Fig. 2.
The shaper is intended to signal the attainment of three pressure limits preset on the scale of the pressure gauge; when
operation of the latter in an explosive atmosphere belonging to category 4, group A.
The shaper consists of two identical parts. Let us consider one of them. It includes an amplifier using transistor \(T_1\) of type P16, an electronic relay using transistor \(T_3\) of type P26, and an MKU-48 relay. Both triodes operate in switching mode, which minimizes the effect of the spread in triode parameters and reduces the power dissipated in the transistors.
Fig. 1. Block diagram of the shaper: 1—device with contactless signaling; 2—output circuit.
Fig. 2.
In the normal state, triode \(T_1\) is open, while \(T_3\) is closed by the voltage arising when the collector current of transistor \(T_1\) flows through resistance \(R_5\). Indeed,
\[ U_{\mathrm{b}eT_3} = R_5 (I_{\mathrm{k}T_1} - I_{\mathrm{d}}) \]
and, for \(I_{\mathrm{k}T_1} > I_{\mathrm{d}}\), what was stated above is valid.
When contact \(K\), located in the manometer, is closed to position 1, the current through \(T_1\) decreases sharply, the voltage at the base of \(T_2\) becomes negative, and it passes into the saturation state. Relay 1 operates and gives a signal that the permissible limit has been exceeded.
The second half of the circuit, using transistors \(T_2, T_4\), operates analogously.
When contact \(K\) is closed to position 3, both relays operate.
Triodes \(T_1\) and \(T_2\) have a common emitter resistance \(R_1\). It serves for more reliable cutoff of triodes \(T_1\) and \(T_2\) when switch \(K\) is closed in one of its three positions.
The circuit is powered from two voltage sources, with \(U_1\) implemented without a filter. This determines the increased values of the cutoff voltage of triodes \(T_3\) and \(T_4\) (from \(1.5\ \mathrm{V}\) and above).
Data for the electrical contact circuit: a) voltage at open contacts \(0.2 \div 0.3\ \mathrm{V}\); b) current with closed contacts \(0.4 \div 0.5\ \mathrm{mA}\).
The shaper has undergone tests at VOSTNII for intrinsic safety, where a positive result was obtained.
The FIPEKM-1 device may be used as an intrinsically safe signaling apparatus for any 2- or 3-position instrument, provided that the resistance of the signaling line does not exceed \(50\ \Omega\).
REFERENCES
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V. A. Khorunzhii, Yu. M. Ribas, S. S. Nedosekov. Explosion-Proof Electrical Equipment. Gosenergoizdat, 1962.
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Rules for the Manufacture of Explosion-Proof Electrical Equipment. Gosenergoizdat, 1963.