Need help understanding HP10544 osc oven circuit.
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From: Jim Thompson on 27 May 2007 13:35 On Sun, 27 May 2007 10:16:48 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On 26 May 2007 21:09:33 -0700, MooseFET <kensmith(a)rahul.net> wrote: > >>On May 26, 8:21 pm, John Larkin >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Sat, 26 May 2007 21:23:46 -0400, Jim Flanagan >> >>Also R11 and Q4 seems to be drawn wrong. > > >Yeah. The PNP should point the other way. Weird. > >Maybe Jim can check and see how it's actually built. > >SRS sells some clones of the old HP ocxo boxes, with nice SC-cut >rocks. Their stability and phase noise are impressive, but their >thermal design is bizarre. They use TO-220 voltage regulators as >heaters, and it looks to me like whoever designed the loop didn't >really understand the dynamics, so they used a proportional-only loop >with fairly low gain, then added feedforward compensation from an >ambient temp sensor to improve temperature regulation. > >John > I can't seem to retrieve this thread's references, but it sounds like an inverted bipolar device used for AGC. Can someone repost the schematic? ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | America: Land of the Free, Because of the Brave
From: John Larkin on 27 May 2007 14:15 On Sun, 27 May 2007 10:35:45 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Sun, 27 May 2007 10:16:48 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On 26 May 2007 21:09:33 -0700, MooseFET <kensmith(a)rahul.net> wrote: >> >>>On May 26, 8:21 pm, John Larkin >>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> On Sat, 26 May 2007 21:23:46 -0400, Jim Flanagan >>> >>>Also R11 and Q4 seems to be drawn wrong. >> >> >>Yeah. The PNP should point the other way. Weird. >> >>Maybe Jim can check and see how it's actually built. >> >>SRS sells some clones of the old HP ocxo boxes, with nice SC-cut >>rocks. Their stability and phase noise are impressive, but their >>thermal design is bizarre. They use TO-220 voltage regulators as >>heaters, and it looks to me like whoever designed the loop didn't >>really understand the dynamics, so they used a proportional-only loop >>with fairly low gain, then added feedforward compensation from an >>ambient temp sensor to improve temperature regulation. >> >>John >> > >I can't seem to retrieve this thread's references, but it sounds like >an inverted bipolar device used for AGC. > >Can someone repost the schematic? > > ...Jim Thompson http://www.leapsecond.com/museum/10544/ I actually meant that Jim Flanagan might check the actual oscillator so see how the heater driver PNP works. John
From: MooseFET on 27 May 2007 16:24 On May 27, 10:16 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On 26 May 2007 21:09:33 -0700, MooseFET <kensm...(a)rahul.net> wrote: > > >On May 26, 8:21 pm, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> On Sat, 26 May 2007 21:23:46 -0400, Jim Flanagan [.....] > SRS sells some clones of the old HP ocxo boxes, with nice SC-cut > rocks. Their stability and phase noise are impressive, but their > thermal design is bizarre. They use TO-220 voltage regulators as > heaters, and it looks to me like whoever designed the loop didn't > really understand the dynamics, so they used a proportional-only loop > with fairly low gain, then added feedforward compensation from an > ambient temp sensor to improve temperature regulation. That is very strange. SRS seems to know what they are doing in the other stuff they do. I can even see an argument for using a 3 pin regulator as the heater. They give a huge current gain, are self protecting and don't have their own tempco. The components needed for a PID controller wouldn't add much to the size of the circuit. These days op-amps with very low bias currents can be obtained easily so the capacitors don't have to be huge.
From: Fred Bloggs on 29 May 2007 07:53 John Larkin wrote: > On Sat, 26 May 2007 21:23:46 -0400, Jim Flanagan > <jflan(a)tampabay.rr.com> wrote: > > >> Hi - >> >> Recently, I acquired an HP ovenized oscillator (HP10544A)which was >> missing the proportional oven controller. I found the schematic >> for the oscillator at the following link: >> http://www.leapsecond.com/museum/10544/ >> >> >> After building the oven controller on a small PCB, I purposely >> disabled the unijunction oscillator stage initially, in order to >> test the controller. My thought was that the switching supply (if >> you want to call it that) section was just to make the the oven >> controller more efficient. With the oscillator disabled, I found >> that the oven would oscillate itself. From a room temp start, the >> oscillator oven would get to temp then shut itself off, then repeat >> at about a .1hz rate. It wasn't until the oscillator section was >> enabled, that the oven would work correctly. By correctly, I mean >> that as the oven approaches it's set point temperature, the op amp >> section would go into its linear mode. This is apparent as the >> heater current begins to decrease from about 500mA to about 180mA. >> >> I would appreciate if someone would take a look at this circuit, in >> terms of the oven controller, and help me understand exactly how >> the UJT oscillator is functioning in this closed thermal system. >> Also, I would appreciate some input as to how an simulate a thermal >> system like this in spice. I simply don't understand how to >> simulate the thermal feedback portion. > > > > If the ujt is off, the loop gain is very high and the thing pretty > much works in bang-bang mode. A very small change in opamp output > will slam the heater full on or full off. Ummmm, looks like U1 is integrating the thermistor bridge error with a 0.001Hz time constant and ~40dB gain, so hard to visualize a "slam" on/off action in that circuit. > > The Q1-Q2 differential pair compares the opamp output to the swatooth > created by the ujt. So the amp output has to span a roughly 7 volt > range to move the heater from full off to full on, which is > effectively a much lower gain. Ummm, since the Q4 current gain is so high, U1 is required to inject just a few uA into Q1 base for full-on of the Darlington. There is not going to be much of a "span" about this Q1 base voltage threshold. > > One less obvious advantage of pwm, as compared to a linear system, it > that it makes heater power linear on error. A linear voltage or > current drive into a heater is a square function. The UJT will be oscillating at something around 4KHz, and its purpose is to chop the Q4 drive to minimize power dissipation, nothing exotic there in the way of control loop processing. The funny labeling on the heater wires and the diode in Q4 lead me to suspect the heater drive may be AC...but then the color coding makes me think it should not be.
From: MooseFET on 29 May 2007 11:26
On May 29, 4:53 am, Fred Bloggs <nos...(a)nospam.com> wrote: [....] > >>http://www.leapsecond.com/museum/10544/ [....] > Ummmm, looks like U1 is integrating the thermistor bridge error with a > 0.001Hz time constant and ~40dB gain, so hard to visualize a "slam" > on/off action in that circuit. How do you get 0.001Hz? 51.1K * 2 uF -> 1.55Hz 5.6M * 2 uF -> 0.014Hz The latter being the zero in the PI controller, I'd expect the gain cross over to be near that point. [....] > Ummm, since the Q4 current gain is so high, U1 is required to inject > just a few uA into Q1 base for full-on of the Darlington. There is not > going to be much of a "span" about this Q1 base voltage threshold. It is the voltage on the base of Q1 that matters here. Q2 is fed with a ramp from C1. |