MA09 Switch Heater Test Results

The switch heater output is specified 0-100 mA at 100 Ohm, which gives a maximum heater power of 1 W. The MA09 switch heater resistivity is 205 Ohm. As the current source has a limited voltage (17 V), the full current over the heater is no longer 100 mA, but only 83 mA. However, together with the increased resistivity, we get an maximum power of 1.41 W.

• Without lambda stage (coil at 4.2 K), a heater power of 0.81 W (13 V x 63 mA) is needed for switching.
• With lambda stage (coil at 2.3 K), a heater power of 1.06 W (14.7 V x 72 mA) is needed for switching.
• With the coil at 2.3 K it takes about 5 seconds from starting the heater at maximum power (1.41 W) until the switch goes off (therefore the usual 30 sec. delay is very conservative).