Update Content - 2021-02-07

content/book/morrison16_groun_shiel.md

@@ -8,7 +8,7 @@ Tags
 : [Electronics]({{< relref "electronics" >}})
 
 Reference
-: ([Morrison 2016](#orgdb34704))
+: ([Morrison 2016](#orgc3a94fb))
 
 Author(s)
 : Morrison, R.
@@ -51,7 +51,7 @@ This displacement current flows when charges are added or removed from the plate
 
 ### Field representation {#field-representation}
 
-<a id="orgb7f2b7d"></a>
+<a id="orgbb971cb"></a>
 
 {{< figure src="/ox-hugo/morrison16_E_field_charge.svg" caption="Figure 1: The force field lines around a positively chaged conducting sphere" >}}
 
@@ -64,18 +64,18 @@ This displacement current flows when charges are added or removed from the plate
 
 ### The force field or \\(E\\) field between two conducting plates {#the-force-field-or--e--field-between-two-conducting-plates}
 
-<a id="org9a5dc2a"></a>
+<a id="org0a58e51"></a>
 
 {{< figure src="/ox-hugo/morrison16_force_field_plates.svg" caption="Figure 2: The force field between two conducting plates with equal and opposite charges and spacing distance \\(h\\)" >}}
 
 
 ### Electric field patterns {#electric-field-patterns}
 
-<a id="org79f77b7"></a>
+<a id="org2812c15"></a>
 
 {{< figure src="/ox-hugo/morrison16_electric_field_ground_plane.svg" caption="Figure 3: The electric field pattern of one circuit trace and two circuit traces over a ground plane" >}}
 
-<a id="org5199523"></a>
+<a id="orge3117ef"></a>
 
 {{< figure src="/ox-hugo/morrison16_electric_field_shielded_conductor.svg" caption="Figure 4: Field configuration around a shielded conductor" >}}
 
@@ -88,7 +88,7 @@ This displacement current flows when charges are added or removed from the plate
 
 ### The \\(D\\) field {#the--d--field}
 
-<a id="org6d533a1"></a>
+<a id="orgd76a948"></a>
 
 {{< figure src="/ox-hugo/morrison16_E_D_fields.svg" caption="Figure 5: The electric field pattern in the presence of a dielectric" >}}
 
@@ -148,9 +148,9 @@ In a few elements, the atomic structure is such that atoms align to generate a n
 The flow of electrons is another way to generate a magnetic field.
 
 The letter \\(H\\) is reserved for the magnetic field generated by a current.
-Figure [6](#org4c94f50) shows the shape of the \\(H\\) field around a long, straight conductor carrying a direct current \\(I\\).
+Figure [6](#org198efb1) shows the shape of the \\(H\\) field around a long, straight conductor carrying a direct current \\(I\\).
 
-<a id="org4c94f50"></a>
+<a id="org198efb1"></a>
 
 {{< figure src="/ox-hugo/morrison16_H_field.svg" caption="Figure 6: The \\(H\\) field around a current-carrying conductor" >}}
 
@@ -167,7 +167,7 @@ Ampere's law states that the integral of the \\(H\\) field intensity in a closed
 \boxed{\oint H dl = I}
 \end{equation}
 
-The simplest path to use for this integration is the one of the concentric circles in Figure [6](#org4c94f50), where \\(H\\) is constant and \\(r\\) is the distance from the conductor.
+The simplest path to use for this integration is the one of the concentric circles in Figure [6](#org198efb1), where \\(H\\) is constant and \\(r\\) is the distance from the conductor.
 Solving for \\(H\\), we obtain
 
 \begin{equation}
@@ -179,7 +179,7 @@ And we see that \\(H\\) has units of amperes per meter.
 
 ### The solenoid {#the-solenoid}
 
-The magnetic field of a solenoid is shown in Figure [7](#org7682896).
+The magnetic field of a solenoid is shown in Figure [7](#org7535570).
 The field intensity inside the solenoid is nearly constant, while outside its intensity falls of rapidly.
 
 Using Ampere's law \eqref{eq:ampere_law}:
@@ -188,7 +188,7 @@ Using Ampere's law \eqref{eq:ampere_law}:
 \oint H dl \approx n I l
 \end{equation}
 
-<a id="org7682896"></a>
+<a id="org7535570"></a>
 
 {{< figure src="/ox-hugo/morrison16_solenoid.svg" caption="Figure 7: The \\(H\\) field around a solenoid" >}}
 
@@ -196,10 +196,10 @@ Using Ampere's law \eqref{eq:ampere_law}:
 ### Faraday's law and the induction field {#faraday-s-law-and-the-induction-field}
 
 When a conducting coil is moved through a magnetic field, a voltage appears at the open ends of the coil.
-This is illustrated in Figure [8](#org431ab1d).
+This is illustrated in Figure [8](#orgd2dee77).
 The voltage depends on the number of turns in the coil and the rate at which the flux is changing.
 
-<a id="org431ab1d"></a>
+<a id="orgd2dee77"></a>
 
 {{< figure src="/ox-hugo/morrison16_voltage_moving_coil.svg" caption="Figure 8: A voltage induced into a moving coil" >}}
 
@@ -237,7 +237,7 @@ The unit of inductance if the henry.
 
 </div>
 
-For the  coil in Figure [7](#org7682896):
+For the  coil in Figure [7](#org7535570):
 
 \begin{equation} \label{eq:inductance\_coil}
 V = n^2 A k \mu\_0 \frac{dI}{dt} = L \frac{dI}{dt}
@@ -432,24 +432,142 @@ Strain-gauge configuration, thermocouple grounding, and charge amplifiers are di
 
 ### Introduction {#introduction}
 
+This chapter is devoted to analog circuits that operate below 100kHz.
+The techniques that are described can be applied to audio amplifiers, power supplies as well as instrumentation.
+
+The availability of integrated circuits has simplified many aspects of analog circuit design.
+Instrumentation must often handle long signal lines, reject ground potential differences, and maintain circuit stability.
+
+The general problem of analog design is called signal conditioning, which includes gain, filtering, offsets, bridge balancing, common-mode rejection, transducer excitation and calibration.
+Once a signal has sufficient resolution and the bandwidth has been controlled, the signal can be digitized and transmitted over a digital link to a computer.
+This chapter treats the problems of conditioning signals before they are sampled and recorded.
+
 
 ### Instrumentation {#instrumentation}
 
+There are many transducers that can measure temperature, strain, stress, position and vibration.
+The signals generated are usually in the milli-volt range and must be amplified, conditioned, and then recorded for later analysis.
 
-### History {#history}
+<div class="important">
+  <div></div>
+
+It can be very difficult to verify that the measurement is valid.
+For example, signals that overload an input stage can produce noise that may look like signal.
+
+</div>
+
+<div class="definition">
+  <div></div>
+
+1.  **Reference Conductor**.
+    Any conductor used as the zero of voltage.
+    If a signal is measured with respect to a conductor called ground, it becomes the reference signal conductor.
+    In an analog circuit, there may be several reference conductors.
+2.  **Signal common / Signal ground**
+    A signal reference conductor.
+3.  **Balance signal(s)**.
+    Two signals measured with respect to a reference conductor whose sum is always zero.
+4.  **An unbalanced signal / A single-ended signal**.
+    A single voltage measured with respect to a reference conductor.
+5.  **Common-mode voltage**.
+    The average interfering voltage on a group of signal conductors measured with respect to a reference conductor.
+6.  **Normal-mode signal**.
+    The signal of interest.
+7.  **Differential signal / Difference signal**.
+    The voltage difference of interest.
+8.  **Instrumentation amplifier**.
+    A general-purpose differential amplifier with bandwidth from DC to perhaps 100kHz and variable gains from 1 to 5000.
+
+</div>
 
 
 ### The basic shield enclosure {#the-basic-shield-enclosure}
 
+Consider the simple amplifier circuit shown in Figure [9](#orgd60f7ec) with:
+
+-   \\(V\_1\\) the input lead
+-   \\(V\_2\\) the output lead
+-   \\(V\_3\\) the conducting enclosure which is floating and taken as the reference conductor
+-   \\(V\_4\\) a signal common or reference conductor
+
+Every conductor pair has a mutual capacitance, which are shown in Figure [9](#orgd60f7ec) (b).
+The equivalent circuit is shown in Figure [9](#orgd60f7ec) (c) and it is apparent that there is some feedback from the output to the input or the amplifier.
+
+<a id="orgd60f7ec"></a>
+
+{{< figure src="/ox-hugo/morrison16_parasitic_capacitance_amp.svg" caption="Figure 9: Parasitic capacitances in a simple circuit. (a) Field lines in a circuit. (b) Mutual capacitance diagram. (b) Circuit representation" >}}
+
+It is common practice in analog design to connect the enclosure to circuit common (Figure [10](#org412bfcb)).
+When this connection is made, the feedback is removed and the enclosure no longer couples signals into the feedback structure.
+The conductive enclosure is called a **shield**.
+Connecting the signal common to the conductive enclosure is called "**grounding the shield**".
+This "grounding" usually removed "hum" from the circuit.
+
+<a id="org412bfcb"></a>
+
+{{< figure src="/ox-hugo/morrison16_grounding_shield_amp.svg" caption="Figure 10: Grounding the shield to limit feedback" >}}
+
+Most practical circuits provide connections to external points.
+To see the effect of making a _single_ external connection, open the conductive enclosure and connect the input circuit common to an external ground.
+Figure [11](#org5d67d92) (a) shows this grounded connection surrounded by an extension of the enclosure called the _cable shield_.
+A problem can be caused by an incorrect location of the connection between the cable shield and the enclosure.
+In Figure [11](#org5d67d92) (a), the electromagnetic field in the area induces a voltage in the loop and a resulting current to flow in conductor (1)-(2).
+This conductor being the common ground that might have a resistance \\(R\\) or \\(1\,\Omega\\), this current induced voltage that it added to the transmitted signal.
+Our goal in this chapter is to find ways of keeping interference currents from flowing in any input signal conductor.
+To remove this coupling, the shield connection to circuit common must be made at the point, where the circuit common connects to the external ground.
+This connection is shown in Figure [11](#org5d67d92) (b).
+This connection keeps the circulation of interference current on the outside of the shield.
+
+There is only one point of zero signal potential external to the enclosure and that is where the signal common connects to an external hardware ground.
+The input shield should not be connected to any other ground point.
+The reason is simple.
+If there is an external electromagnetic field, there will be current flow in the shield and a resulting voltage gradient.
+A voltage gradient will couple interference capacitively to the signal conductors.
+
+<div class="important">
+  <div></div>
+
+An input circuit shield should connect to the circuit common, where the signal common makes its connection to the source of signal.
+Any other shield connection will introduce interference.
+
+</div>
+
+<div class="important">
+  <div></div>
+
+Shielding is not an issue of finding a "really good ground".
+It is an issue of using the _right_ ground.
+
+</div>
+
+<a id="org5d67d92"></a>
+
+{{< figure src="/ox-hugo/morrison16_enclosure_shield_1_2_leads.png" caption="Figure 11: (a) The problem of bringing one lead out of a shielded region. Unwanted current circulates in the signal lead 2. (b) The \\(E\\) field circulate current in the shield, not in the signal conductor." >}}
+
 
 ### The enclosure and utility power {#the-enclosure-and-utility-power}
 
+When utility power is introduced into an enclosure, a new set of problems results.
+The power transformer couples fields from the external environment into the enclosure.
+The obvious coupling results from capacitance between the primary coil and the secondary coil.
+Note that the secondary coil is connected to the circuit common conductor.
+
+<a id="orgb45b4f3"></a>
+
+{{< figure src="/ox-hugo/morrison16_power_transformer_enclosure.png" caption="Figure 12: A power transformer added to the circuit enclosure" >}}
+
 
 ### The two-ground problem {#the-two-ground-problem}
 
 
 ### Instrumentation and the two-ground problem {#instrumentation-and-the-two-ground-problem}
 
+The basic analog problem is to condition a signal associated with one ground reference potential and transport this signal to a second ground reference potential without adding interference.
+
+<a id="org75ed03f"></a>
+
+{{< figure src="/ox-hugo/morrison16_two_ground_problem.svg" caption="Figure 13: The two-circuit enclosures used to transport signals between grounds" >}}
+
 
 ### Strain-gauge instrumentation {#strain-gauge-instrumentation}
 
@@ -462,6 +580,10 @@ Strain-gauge configuration, thermocouple grounding, and charge amplifiers are di
 
 ### The basic low-gain differential amplifier (forward referencing amplifier) {#the-basic-low-gain-differential-amplifier--forward-referencing-amplifier}
 
+<a id="orge28ae4f"></a>
+
+{{< figure src="/ox-hugo/morrison16_low_gain_diff_amp.svg" caption="Figure 14: The low-gain differential amplifier applied to the two-ground problem" >}}
+
 
 ### Shielding in power transformers {#shielding-in-power-transformers}
 
@@ -474,6 +596,24 @@ Strain-gauge configuration, thermocouple grounding, and charge amplifiers are di
 
 ### Signal flow paths in analog circuits {#signal-flow-paths-in-analog-circuits}
 
+<div class="important">
+  <div></div>
+
+Here are a few rule that will help in analog board layout:
+
+1.  Maintain a flow of signal and signal common from input to output.
+    The area between the signal path and the signal reference conductor should be kept small.
+2.  Components associated with the input should not be near output circuit components.
+3.  Power supply connections (DC voltages) should enter at the output and thread back toward the input.
+    This avoids common-impedance coupling (parasitic feedback).
+4.  The greatest attention should be paid to the input circuit geometry.
+    Lead length for components connecting to the input path should be kept short.
+    Another way of describing this requirements is to interconnect the components to minimize the amount of bare copper connected to the input signal path.
+5.  Feedback summing points are critical.
+    Keep lead lengths short at these nodes.
+
+</div>
+
 
 ### Parallel active components {#parallel-active-components}
 
@@ -483,6 +623,14 @@ Strain-gauge configuration, thermocouple grounding, and charge amplifiers are di
 
 ### Feedback theory {#feedback-theory}
 
+<a id="orgbf57c39"></a>
+
+{{< figure src="/ox-hugo/morrison16_basic_feedback_circuit.svg" caption="Figure 15: The basic feedback circuit" >}}
+
+<a id="org795e24d"></a>
+
+{{< figure src="/ox-hugo/morrison16_LR_stabilizing_network.svg" caption="Figure 16: An LR-stabilizing network" >}}
+
 
 ### Output loads and circuit stability {#output-loads-and-circuit-stability}
 
@@ -501,6 +649,44 @@ Strain-gauge configuration, thermocouple grounding, and charge amplifiers are di
 
 ### Charge converter basics {#charge-converter-basics}
 
+In vibration analysis, piezoelectric sensors are used which are electrically equivalent to a capacitor.
+When a force is exerted to the piezoelectric material, charges or voltage are generated.
+The relationship between charge and voltage is \\(V = Q/C\\) where \\(C\\) is the transducer capacitance.
+
+The voltage on the transducer can be amplifier by a high-impedance amplifier.
+The input cable capacitance attenuates the input signal and this makes calibration a function of cable length.
+The preferred method of amplifying signals from piezoelectric transducers is to measure charge generation and not voltage generation.
+The charge is first converted to a voltage and the voltage is then amplified.
+This type of instrument is called a **charge amplifier**.
+
+The basic feedback around an operational amplifier usually involves two resistors.
+The voltage gain is simply the ratio of the two resistors.
+If the resistors are replaced by capacitors, the gain is the ratio of reactances.
+This feedback circuit is called a **charge converter**.
+The charge on the input capacitor is transferred to the feedback capacitor.
+If the feedback capacitor is smaller than the transducer capacitance by a factor of 100, then the voltage across the feedback capacitor will be 100 times greater than the open-circuit transducer voltage.
+This feedback arrangement is shown in Figure [17](#org964dc8b).
+The open-circuit input signal voltage is \\(Q/C\_T\\).
+The output voltage is \\(Q/C\_{FB}\\).
+The voltage gain is therefore \\(C\_T/C\_{FB}\\).
+Note that there is essentially no voltage at the summing node \\(s\_p\\).
+
+<div class="important">
+  <div></div>
+
+A charge converter does not amplifier charge.
+It converts a charge signal to a voltage.
+
+</div>
+
+<a id="org964dc8b"></a>
+
+{{< figure src="/ox-hugo/morrison16_charge_amplifier.svg" caption="Figure 17: A basic charge amplifier" >}}
+
+<a id="orgdd200ce"></a>
+
+{{< figure src="/ox-hugo/morrison16_charge_amplifier_feedback_resistor.svg" caption="Figure 18: The resistor feedback arrangement to control the low-frequency response" >}}
+
 
 ### DC power supplies {#dc-power-supplies}
 
@@ -542,6 +728,55 @@ Solar winds can disrupt power distribution and damage oil pipelines.
 
 ### Semantics {#semantics}
 
+Here are the key words used by a power engineer as defined by the NEC:
+
+Ground
+:
+
+
+Equipment ground
+:
+
+
+The grounded conductor
+:
+
+
+The ungrounded conductor
+:
+
+
+Neutral
+:
+
+
+Isolated ground
+:
+
+
+Service entrance
+:
+
+
+Grounding electrode system
+:
+
+
+Feeder circuit
+:
+
+
+Branch circuit
+:
+
+
+Separately derived power
+:
+
+
+Listed equipment
+:
+
 
 ### Utility power {#utility-power}
 
@@ -699,6 +934,36 @@ Methods for limiting field penetration into and out of a screen are offered.
 
 ### Cables with shields {#cables-with-shields}
 
+In analog work, an aluminum foil is often used as a shield around a cable.
+The inside of the aluminum foil is anodized to provide protection against corrosion.
+Because it is difficult to terminate the foil at the cable ends, a drain wire is provided on the outside of the cable foil.
+This drain wire is made of multistranded tinned copper wires that make contact with the foil along the length of the cable.
+If the foil should break, the drain wire connects the segments together.
+
+In audio work, where a cable carries a microphone signal, the cable can be a shielded single conductor.
+In instrumentation, best practice requires that the signal common and the shield be separate conductors.
+
+An aluminum foil over a group of conductors provides an **excellent electrostatic shield at low frequencies**.
+In analog work, the shield should be connected at one end to the reference conductor preferable where it connects to a ground.
+If the drain wire is connected to grounded hardware at both ends, then interference can result.
+Electromagnetic fields in the area will cause current flow in the resulting loop.
+
+A foil seam does not allow current to flow freely around the cable.
+Also the foil doesn't form a very stable geometry.
+For these reasons, foil shields should not be used where the characteristic impedance of the cable needs to be controlled.
+The termination of shields at a hardware interface can be critical.
+A cable terminated by a drain wire allows field energy to penetrate the hardware at the hardware at the connector.
+A woven braid can provide 360 degree termination.
+
+The term coax is generally applied to cable where the characteristic impedance is controller.
+A typical coax is a single conductor surrounded by a shield with a controlled geometry.
+For applications from DC to about 1MHz, the characteristic impedance may not be important.
+Above this frequency, coaxial cables is preferred.
+The manufacturer supplies specifications relating to signal loss at high frequencies.
+
+The characteristic impedance of a transmission line is a function of the conductor geometry and of the dielectric constant.
+To transport RF power without reflections, the source impedance and the terminating impedance must match the line impedance.
+
 
 ### Low-noise cables {#low-noise-cables}
 
@@ -768,4 +1033,4 @@ Methods for limiting field penetration into and out of a screen are offered.
 
 ## Bibliography {#bibliography}
 
-<a id="orgdb34704"></a>Morrison, Ralph. 2016. _Grounding and Shielding: Circuits and Interference_. John Wiley & Sons.
+<a id="orgc3a94fb"></a>Morrison, Ralph. 2016. _Grounding and Shielding: Circuits and Interference_. John Wiley & Sons.