Device Heater Theory Of Operation - Keysight Technologies PD1500A Software Manual

Using the Optional Device Heaters

Device Heater Theory of Operation

If the device heater operated in a pure vacuum, the heating curve would be a
simple straight line -- you apply a certain amount of energy to the heater and it
heats to the desired temperature. But in a real-world test system, there are more
issues involved. The heater heats not only itself, but also the DUT, the aluminum
clamp, plus a small amount of heat is lost to the air.
Therefore, a control circuit applies energy to the heater, monitors its temperature
(via a K-type thermocouple) and tries to regulate at the desired temperature. In
the PD1500A, the temperature is sampled approximately 10 times per second.
The heater itself has a theoretical capacity to heat itself at a rate up to 175  C
per second. In 1/10 of a second then, the heater can raise its temperature
approximately
15  C. So, if you set a small temperature increase, let's say 10  C, then in 1/10 of
a second, the heater can overshoot your desired temperature by 5  C. Again, it is
slightly less than that because heat is transferred to the device, the clamp,
surrounding air, etc.
The heater has no capacity to actively "cool" a device; it can heat the device.
Therefore, to lower the temperature, the system must allow the heater to cool
and allow the heat to dissipate. This may take a few minutes.
If you set a large temperature change, for example, from 22  C to 150  C, then it
may take several seconds to arrive at the desired temperature. Again, there is the
possibility of slight temperature overshoot.
Figure 36 shows the fields in the Hardware Configuration used to set the
Temperature Tolerance and Settling Time. Several temperatures may be set with
a semicolon list (for example, 25;50;100;150).
Temperature
Figure 39 PD1500A Device Heater Timing
120
Tolerance
Settling Time
Time when temperature
is first reached (within range)
Device Heater Theory of Operation
Time when DPT measurement
is actually initiated
Keysight PD1500A Double-Pulse Test System
Time