Siemens Industry 661A2

Series 661 Amplifying Relays are fixed-gain force-balance instruments, which incorporate bias adjustment that amplify pneumatic instrument signals. For example, a 3 to 15 psi signal can be amplified to operate a 3 to 27 psi control valve.

The input pressure signal, acting upon the effective area of the upper diaphragm, produces a force opposed by the force produced by the output pressure applied over the effective area of the lower diaphragm and by a manually-set (constant) spring force. Any imbalance in the opposing forces will operate the pilot valve to throttle supply air to change the output until rebalance is achieved.

Plus or minus biasing of the input signal is accomplished by changing the setting of the upper biasing spring, which alters the net spring force on the diaphragm assembly.

Product Highlights

• Fixed-gain force and bias adjustment mechanisms amplify pneumatic instrument signals to provide control circuit design flexibility.
• Maximum Supply Pressure: 80 psig (550 kPa)
• Maximum Range Limits for Input or Output: 80 psig
• Direct Acting Bias Range: -15 to 30 psi (-100 to 210 kPa)
• Gain: 2
• Minimum Supply Pressure: 1 psi (7 kPa)