Battery drain test on anniversary gift clock

Last month, on June 2, 2015, I celebrated working for Hewlett-Packard/Agilent Technologies/Keysight Technologies for 35 years. During the earlier times of my career, on significant anniversaries such as 10 years or 20 years, employees could choose from a catalog of gifts to have their contributions to the company recognized. That tradition has been discontinued, but I did select a couple of nice gifts over the years. During my HP days, one gift I selected was a clock with a stand shown here:

I have had that clock for decades and it uses a silver oxide button cell battery (number 371). I have to replace the battery about once per year and wondered if that made sense based on the battery capacity and the current drain the clock presents to the battery. I expected the battery to last longer so I wanted to know if I was purchasing inferior batteries. These 1.5 V batteries are rated for about 34 mA-hours. So I set out to measure the current drain using our N6705B DC Power Analyzer with an N6781A 2-Quadrant Source/Measure Unit for Battery Drain Analysis power module installed. Making the measurement was simple…..making the connections to the tiny, delicate battery connection points was the challenging part. After one or two failed attempts (I was being very careful because I did not want to damage the connections), I solicited the help of my colleague, Paul, who handily came up with a solution (thanks, Paul!). Here is the final setup and a close-up of the connections:

I set the N6781A voltage to 1.5 V and used the N6705B built-in data logger to capture current drawn by the clock for 5 minutes, sampling voltage and current about every 40 us. The clock has a second hand and as expected, the current showed pulses once per second when the second hand moved (see Figure 1). Each current pulse looks like the one shown in Figure 2. There was an underlying 200 nA being drawn in between second-hand movements. All of this data is captured and shown below in Figure 3 showing the full 5 minute datalog along with the amp-hour measurement (0.28 uA-hours) and average current measurement (3.430 uA) between the markers.

Given the average current draw, I can calculate how long I would expect a 34 mA-hour battery to last:

                 34 mAh / 3.430 uA average current = 9912.54 hours = about 1.13 years

This is consistent with me changing the battery about every year, so once again, all makes sense in the world of energy and electronics (whew)! Thanks to the capabilities of the N6705B DC Power Analyzer, I now know the batteries I’m purchasing are lasting the expected time given the current drawn by the clock. How much current is your product drawing from its battery?

Let's See the Watchdog TImer in Action

Hi everybody!

It is the end of the month and time for my monthly blog post.

Quite some time ago, my buddy Gary mentioned our watchdog timer protection in a post.  Here is what he had to say:

The watchdog timer is a unique feature on some Agilent power supplies, such as the N6700 series. This feature looks for any interface bus activity (LAN, GPIB, or USB) and if no bus activity is detected by the power supply for a time that you set, the power supply output shuts down. This feature was inspired by one of our customers testing new chip designs. The engineer was running long-term reliability testing including heating and cooling of the chips. These tests would run for weeks or even months. A computer program was used to control the N6700 power supplies that were responsible for heating and cooling the chips. If the program hung up, it was possible to burn up the chips. So the engineer expressed an interest in having the power supply shut down its own outputs if no commands were received by the power supply for a length of time indicating that the program has stopped working properly. The watchdog timer allows you to set delay times from 1 to 3600 seconds. 

(For the whole post click here)

Since Gary wrote that post, we have released the N6900 and N7900 APS units that also include this useful feature.  What I wanted to do was show how to set it up, how to use it,and how to clear it so that everything is a bit more clear.   All of my programming examples in this post will be done using my APS with the VISA-COM IO Library in Visual Basic.

The setup is pretty easy:

        APS.WriteString("OUTP:PROT:WDOG:DEL 5")
        APS.WriteString("OUTP:PROT:WDOG ON")

This sets the watchdog delay to 5 seconds and enables it.  This means that if there is no IO activity (ie your computer hangs up) for 5 seconds, then the unit will go into protect and shut the output down.

Lets say that I have a program that performs a measurement around every second for a minute.  Here is the program:


        APS.WriteString("OUTP:PROT:WDOG:DEL 2")
        APS.WriteString("OUTP:PROT:WDOG ON")

        For i = 0 To 59
            APS.WriteString("MEAS:VOLT?")
            strResponse = APS.ReadString
            Threading.Thread.Sleep(1000)
        Next

        Threading.Thread.Sleep(3000)

        APS.WriteString("STAT:QUES:COND?")
        strResponse = APS.ReadString

 The watchdog delay is set for 2 second so while I run in the loop taking my measurements everything is working great.  After the 3 second wait at the end though, the 2 second watchdog timer comes into effect and the unit goes into the protect state and disables the output.  The response to the questionsable status query is 2048 which corresponds to bit 11 of the register which is defined as "Output is disabled by a watchdog timer protection".  This is the expected result.

My reccomendation to clear the watchdog timer would be to first disable the watchdog timer and then clear the protect.  You can then re-start the watchdog timer when you are ready.

        APS.WriteString("OUTP:PROT:WDOG OFF")
        APS.WriteString("OUTP:PROT:CLE")

The watchdog timer is a pretty cool feature that can perform a pretty useful task.  I hope that this blog post explains what it is and how to use it a bit more.

Arbs! Arbs! Arbs!

Hi everybody,

We have a new intern here and we have recently been talking about the arbitrary waveform capabilities (from now on I will refer to this as arbs)  of our power supplies and I thought that this would make an interesting blog post.  This is a really cool feature that we offer in our products as it give you the ability to create an alternating signal using our DC power supplies.  The two types of arbs are the LIST system and the constant dwell arb.

The LIST arb is a feature that we have in quite a few of our products.  The N6700 family, the N7900 family, and even some of our older power supplies have this feature.  The "Arb" system in the N6705 DC Power Analyzer is similar to the LIST.  These LISTs can contain as many as 512 different points with a timing resolution as low as 1 us.  Each point consists of a voltage or current setting and a time.  The times can be different for each point.  A short example of a programmed LIST is:

VOLT:MODE LIST
LIST:VOLT 10,25,5
LIST:DWEL 5,1,4

In the example above, the voltage will start out at 10 V and stay for 5 seconds, then transition to 25 V for 1 s and then go to 5 V for 4 s.  As you can see there are 3 voltage values with 3 corresponding dwell times.

The second mode for arbs that is only available on the N6705B DC Power Analyzer and the N7900 APS is call the Constant Dwell Arb (CD Arb).  In this mode, you can program as many as 64K points but all of the defined points have the same dwell time.  If we want to do the same waveform as above, we need to choose what will be our dwell time.  Since the smallest dwell I used in my example is 1 s, I will choose that.  Here is what a small part of the code would look like:

VOLT:MODE ARB
ARB:VOLT:CDW:DWEL 1
ARB:VOLT:CDW 10,10,10,10,10,25,5,5,5,5

The code above will produce the same waveform as the LIST example.  CD Arbs can get pretty unwieldy when you have a ton of points but we do offer some tools in our 14585A Control and Analysis software that allow you to import and export csv files to make life a bit easier.

There are advantages and disadvantages to both.  As you can see, in some cases it is easier to program a list since it requires less dwell points and gives you more flexibility with what your dwell can be.  If your waveform has a lot of DC levels in it, then the standard list might work for you.  If you have a long, complex waveform the 64 Kpoints offered in an arb will most likely offer you the best option to replicate your waveform.

Whichever arb you pick, this is a very powerful tool.  I am thinking that I will follow this up at a future date with more information about arbs.  If you have any questions, feel free to leave us some comments.